Demon used to be an aristocrat that was disgusted by the degenerate aristocracy that had no social standing in public. At some aristocrat party, he met and fell in love with a daughter of a Duke, named Elena, who shared the same ideals as Demon and wished to change the way of the nobilities at the time, and they eventually became lovers. Sometimes afterwards, Elena introduced Demon to Giotto, and agreeing to her suggestion, he joined the Vongola family. For sometime, Demon found the Vongola Famiglia perfect and dedicated all his strength to it.
However, over the time, as the Vongola was growing stronger, Giotto started to fear that the Vongola would only bring more enemies and eventually begin fighting for self-interest. Not wanting the Vongola to deviate from their original purpose, Giotto decided to disband their military forces. Demon tried to convince him otherwise, but Giotto still stick to his decision, officially disbanding their military forces. This consequently led their territory open to attack and be invaded by a rival Family, which led to Elena's death. Before she dies in his arms, Elena pleads to Demon to protect the weak together with the Vongola. Triggered by this incident, Demon swore to make the Vongola the strongest Famiglia that will make people fear to defy, believing it would fulfil Elena's last wish. Since then, Demon became a backstabber, annihilating anything and anyone whom he considered a threat that weakened the Vongola behind Primo's back.
In the massive Mafia war between the Vongola and a rival mafia Family, he sets up a trap for Giotto's best friend, Simon Cozzato, who he saw as a weakening factor of Giotto and a threat to the Vongola. Later, at one point, he betrays Giotto himself, due to Giotto's inability to overcome his softness and his own desire to want the Vongola to be stronger than it was at that point, which heavily contradicted the other Guardians' views. He finally came to the conclusion that Giotto was no longer suitable to be the Vongola's boss and forced him to resign from his position. After this betrayal, he was the only one who remained behind in the Family and eventually became Vongola Secondo's Mist Guardian, making him the only Guardian to maintain the position for two generations. Later, at one point, during or after his time as Vongola Secondo's Mist Guardian, he cut off his attachment with his own body and threw it away and began to survive for decades by possessing one person to another, so he could continue living to watch over the Vongola's growth the way that he desired.
7 years prior to the Inheritance Ceremony Arc and during the persecution and childhood of Simon, Demon shot bullets to the bosses' houses that were important to the Vongola and barbarically killed 12 CEDEF members inside an elevator, starting the "Flood of Blood" incident. He left a bullet in the elevator that belonged to Enma's father, Makoto Kozato, and that night, he disguised himself as Iemitsu Sawada and murdered Makoto, his wife, and his daughter, Mami Kozato, sparing his son, Enma Kozato, who he let live to implant hatred for the Vongola within him. Afterwards, he somehow managed to borrow a vessel of one of the Simon Guardians, Julie Kato, and continuously used Julie to control the rest of the Simon members in order to mislead them into fighting the Vongola.
When Tsuna and the others return to the past with Uni to train before the battle with Byakuran, Uni summons Vongola Primo, who tells everyone that the first Guardians of the Vongola will observe them henceforth to see if they were worthy to inherit the Vongola's true power or not. At night, Demon Spade appears from the Vongola Mist Ring to Chrome at the same time as the other First Generation Guardians. Later, when Tsuna and the rest were discussing their success so far, Demon Spade appears outside Tsuna's house and states to himself that Tsuna is unfit to unite the Vongola Famiglia, just like how Primo once was, and disappears.
Mist Guardian Succession Trial Edit
Later, he traps Chrome and the other girls within an illusory bubble of space with limited oxygen. He disguised himself as Chrome and appeared in front of Tsuna and the others, saying that Tsuna was unfit to unite the Vongola Famiglia. Tsuna immediately knew that it wasn't Chrome, causing Demon Spade to drop the disguise and say that Tsuna at least possesses Vongola Hyper Intuition. When Tsuna asked why he did this, he simply stated that he didn't approve of Tsuna and his Guardians. It was revealed that he controlled Chrome to draw out Kyoko and the others in order to force Tsuna and the rest to submit to his will. He goes on to say that Tsuna and the others must become the ideal heirs to the Vongola tradition to save the girls. His version of the Vongola was unparalleled strength and ruthlessness, enough to defeat any and all enemies, a heavy contradiction to the views of the other first-generation guardians. The battle starts after Demon opens a door for the guardians to enter the Kokuyo Land building, but afterwards makes the entire building disappear so as to prevent any intervention. He manages to separate the group and attempts to individually mold them into the type of people he wants them to be.
As the battle continues, Demon becomes extremely frustrated at the Guardians' resolve. He reveals to Tsuna that it wasn't the Vongola Secondo that forced Giotto to step down, but him. His illusion was broken by the combined efforts of the Guardians and the Arcobaleno. However, he refused to pass on the inheritance, and claimed that it was time he got serious. He then challenged Tsuna to a one-on-one battle with him directly, even though it wasn't how he preferred to fight. Tsuna then battled him without interference. During the battle, Demon revealed that he had served the Vongola for two generations and he didn't want the Vongola to fall apart because of the foolish thoughts of a mere boy (Tsuna). Tsuna said that he understood his feelings, but he only wanted the power for the sake of his friends, much to Demon Spade's annoyance. After that, he directed his attacks to Uni and the girls but Tsuna stood in his way. He then trapped Tsuna in an illusion that hid his presence. Tsuna used his X-Burner to try to attack him and dispel the mist, but, instead, the attack was redirected to Chrome Dokuro and the girls because of Demon Spade's trap. However, Mukuro immediately switched places with Chrome and blocked the attack with his trident, shocking Demon.
After some conversation with Mukuro, Tsuna attacked him again and finally was able to use his X-Burner on him with the help of Mukuro. Since Demon had no body to begin with, the X-Burner didn't kill him, and he appeared again, stating that he no longer had any intention to fight since he knew it would be pointless. He instead directed his attention to Mukuro and questioned his motive, to which Mukuro replied by answering that Tsuna is his target and he planned to destroy the Mafia and conquer the world, surprising Demon. Seeing Mukuro's concern for Chrome yet at the same time apathetic for the Kyoko and the others' lives is befitting characteristic for the role of Mist Guardian, Demon decided to deem him worthy as Mist Guardian. Rebuking that form of address, Mukuro disappeared and Chrome was returned to normal.
Shortly afterwards, Giotto appears and praises Demon for fulfilling his duty, to which he replies that Giotto never changes. He then deems Chrome worthy and gives her his inheritance. Later, he is seen looking at his pocket watch with Giotto appearing besides him as the latter comments that he still keeps the pocket watch with their vow of eternal friendship written in Italian engraved on the lid. Giotto says that his feeling regarding that matter hasn't changed, making Demon comment that he would forever be a fool, which is why he disappointed him in the end. He states his doubts they will cross paths again, before bidding Giotto farewell and going back inside the Vongola Ring.
While Tsuna fought Byakuran, he appeared, along with Giotto and the other guardians, from Mukuro's Vongola Ring after witnessing Tsuna's resolve. He expressed his disappointment that even after being driven into corner, Tsuna still refuses to change his ideal, and commented that kind of ideal was useless for Vongola since Vongola doesn't need such weakness.
Julie Kato turned out to be possessed by Demon after he revealed that he was the one who devised the entire war between the Vongola and the Simon and that he was the one who made the illusionary organs for Chrome when she was on the island. He revealed his plan that he wishes for the annihilation of the Vongola Family and plans to use Chrome as his tool to take over Mukuro's body. When Chrome refused to cooperate, he made her obey by controlling her mind with the power of his right eye. Later, he's seen again after Chrome changed her clothes to the Simon middle school uniform and ordered her to be with him at all times so he will be able to quickly get used to controlling her mind as he changed back into Julie.
Kyoya Hibari vs. Adelheid Suzuki Edit
When Adelheid challenged Hibari, he along with Chrome watched from afar as he says that Tsuna, who has inherited the thick blood of Vongola Primo, is a dangerous factor of the Vongola. After Adelheid is defeated and the fourth key was shown, Demon finally reveals himself to Tsuna and the others, including his plan of using the Simon to overthrow the Vongola so he could change the Vongola to the way he desires, and that he was the one who set a trap for Simon Cozzato that would eventually lead to his death and took Julie as his vessel to manipulate the current Simon. In the middle of it, Kaoru arrives and stabs Demon from behind out of anger. This turns out he used illusions with the power of Desert Flame as he stabs Kaoru from behind, easily overpowers him. He was about to kill Kaoru, but Yamamoto arrives and protect him, leading a brief fight with Yamamoto. During the fight, Kaoru protects Yamamoto from Demon Spade's attack and was imprisoned because he had lost his pride, which leads the Vindice to reveal the next key that shows Giotto had found out of Demon Spade's plan and sent his Guardians to save Cozzato and his Family. This revelation shocks Demon as he couldn't find a single trace of Cozzato's existence now it was revealed that Cozzato was survived the war. However, this doesn't stop Demon to continue with his plan and he reassumes his fight with Yamamoto. With the Rain Vongola Gear and Demon Spade's inability to use his full power due to the lack of compatibility with Julie's body, Yamamoto able to dispel Demon Spade's illusion, forcing Demon to retreat with Chrome.
Vs. Mukuro Rokudo Edit
The next day, in Enma's throne, Demon disguised as Julie again, enraged Enma further by telling him Adelheid and Kaoru's defeat at the hands of the Vongola, causing Enma to be consumed by his Earth Simon Ring and reborn as killing machine. He changed back to himself and commented that now there are no voice that could reach him and he leaves Enma to defeat Tsuna. He went back to Chrome who he had tied up so he could undo his mind control on her without any resistance. When Chrome panic, he assured her that he will let her to meet Mukuro by removing the barrier so Mukuro could come to save her. He revealed that is the perfect time because Julie's Desert Simon Ring is fully awakened and he able to go with his plan to fight Mukuro with Chrome as the bait. He removed the barrier of the island and removes Chrome's illusionary organs again, causing her stomach to sink. He shouts at Mukuro to appear or Chrome will die. Shortly, as he had hoped, Mukuro appears in Chrome's stead out of anger and he comments that with one glance, he could tell that he was a skillful illusionist, to which Mukuro replies that in a glance he could tell that Demon is the epitome of everything he hates, which amuses Demon and offeres to have some tea to calm himself down as Mukuro are furious but Mukuro declined and claimed that he from now will take him with him into hell. After witnessing the Sixth key, he clashes with Mukuro, commenting that he's better than he could have thought and it's about time that he shows how serious he could be, to which Mukuro replies that he wouldn't want any other way.
As the battle continues, Demon brought out a deck of cards, to which Mukuro mocks that, he now starts playing useless cards. Demon replies that it's not just ordinary cards; he has two jokers, which are his Mist Flame and Julie's Desert Flame, thus, making his illusions much stronger than Mukuro's. Mukuro knew that and changed the ore of the Mist to the Mist Earring Version X and reveals his Cambio Forma, a Monk's Staff. Mukuro traps Demon within his illusions and Demon disguised himself as Chrome and uses his cards to counter it, changing the cards into forms of Ken, Chikusa, Fran, and M.M, thinking that it will make Mukuro's concentration dull and make him hesitate while they fight. However, without pause, Mukuro stabs the illusions and states that he doesn't consider them comrades that he shares emotional bonds with, and that he's on his own right now, surprising Demon. Demon asks what does he mean because Mukuro seems upset when he taken and manipulated Chrome. Mukuro answers that he doesn't like being controlled. Demon thought in his mind that when illusionist possesses someone, normally they able to share their senses but realizes that Mukuro's case is different level, it crosses beyond emotions, unity, a complete absolute bond, making him comments that Mukuro and his subordinates are an absurd group of guys before losing consciousness, seemingly defeated but not before he thanked Mukuro.
However, it turned out that while Mukuro possessed Chrome, Demon took it as the opportunity to take over Mukuro's soulless body in Vindice Prison, causing the connection between Mukuro's body to sever, which resulted in Mukuro unable to go back to his own body and using his remaining power to possess Mukuro. This made Mukuro and the others realizes that everything had been all according to Demon Spade's plan; Demon lay his hands on Chrome in order to lure out Mukuro and intentionally lose his battle with him so that he could possess Mukuro's soulless body before Mukuro does with the fully awakened Simon Desert Ring. In Vindice Prison, Demon—now possessing Mukuro's body - frees himself from the chains binding him within the water tank. Soon after, Demon arrived back in Simon Island in front of Tsuna and the others, Vindice states that Demon who has now taken over Mukuro's body has also obtained the same attribute as the Vindice. Demon decided that it's about time to end Tsuna's Family generation.
Vs. Kyoya Hibari Edit
When they finally start the battle, Demon in the blink of an eye was already in front of Tsuna and the others and sent Gokudera, Yamamoto, Lambo, and Julie to his illusionary worlds with the power of his Joker cards that he had created from the same attribute as the Vindice when he arrived but not before they pushed Tsuna, Chrome, and Enma away from the explosion. He explained that he intended to use it to pass down the tragic death of the tenth Vongola Family to the next Vongola generations after the tenth generation Vongola were annihilated. Shortly after, Hibari challenged him into one-on-one battle as he said that the story they will pass on will be the story of his death, making Demon commented that he just like the first Cloud Guardian, Alaudi and accepted his challenge. Demon revealed to them that he had gained the power of Six Simon Flames from the Simon Rings that he had stolen from Vindice Prison along with Mukuro's body. When Hibari strikes him again, his attack was blocked by Demon who's also using the same Vongola Gear as Hibari, much to everyone's surprise.
Demon revealed that it was because of his attribute, which Mukuro confirmed as Mist. Demon admitted this and revealed the Earrings of the Mist, Chrome and Mukuro's Vongola Gear. Reborn came to the conclusion that it was all just illusions. Hibari, upon the realization that Demon Spade's Gear was fake, charged at Demon and attacked him furiously, gravely injuring him, but Demon countered back by using Ryohei's Maximum Sunshine counter and purposely missing Hibari as he threw a card that sent Hibari into his illusionary world like the other Guardians, thus sparing his life and claiming that he would tell of the tale of Demon Spade's rise in the new Vongola. Enraged by this, Tsuna changed into Hyper Dying Will Mode and attacked Demon but had difficulty when Demon used Lambo and Gokudera's Vongola Gear. However, Enma interfered and joined Tsuna to fight Demon. The two boss attack Demon with a combination but he defend himself with the Bone Loops of the Buckle of the Storm Version X.
Final Battle Edit
Realizing the power of Tsuna and Enma's combination, Demon decided to get serious and able to overwhelm both of them by using six Simon Rings and Vongola Gears all at once and multiplied himself into six that separated Tsuna and Enma, preventing them to coordinate their attack together and stop Chrome from assisting them. When Demon revealed that to inflict normal damage they have to attack six of him in same time, Enma decided to catch all six Demon with his black holes, gathering them together and tell Tsuna to incinerate Demon into ash along with himself as there are no other option left in order to defeat him. Demon momentarily panic since he had used most of his flames to escape Enma's black holes until he realizes Tsuna's inability to sacrifice his comrade and taunts him to make Tsuna hesitant until Enma's flames weaken. But this foiled when Chrome protects Enma by using her Mist Barrier in full power that also supports by Mukuro, making Tsuna convinced to shoot XX Burner. Demon shouts at him to wait and don't shoot but Tsuna ignores this and shoot him with XX Burner in full power.
However, Demon survived the attack and disguised as Enma, pretending to help Tsuna stand before kicked him away, shocking everyone since not only alive, but Demon still had energy to fight despite his injuries. He begun to broke Tsuna's bones and ready to deliver finishing blow. But before he could, Enma's Simon Ring combined with Tsuna's Vongola Ring, giving Tsuna energy to turn into Hyper Dying Will Mode and gained Enma's Earth Flame as well as Giotto and Cozzato's oath's Flames. Tsuna immediately overpowered Demon, making Demon heavily injured. Refused to lose, Demon healed himself with his healing ability and increased his entire Flames, preparing to fight Tsuna for the last time.
Demon reveals that he had watched the Vongola for years to ensure that the Vongola become the strongest Mafia Family, and he decides to escape using the Vindice's eight element Flame. However, Tsuna sees through his plan and holds him down with Enma's Earth Flames, making him unable to move. Tsuna was about to incinerate Demon, but against doing so and instead asks him to surrender and atone for his sins. Refusing to back down, Demon uses the Flame of the Vindice and is able to deflect the Flames of the Earth's abilities. As he clash with Tsuna for the last time, the two uses all their flames against each other, it is then while they collided, Demon escapes and gives up Mukuro's body, and flew off in his illusion form making a dash for the portal he created with the Vindice Flames, it's then, however, that Bermuda crushes his portal and states that only those with a physical body could use the Flame of the Vindice as stated by the law. With Demon defenseless and has no way to run, Tsuna then blasts Demon with his X-Burner, killing him in the process. After being defeated, something left behind as Demon Spade's soul disappeared, revealed to be a pocket watch and Demon Spade's treasure as stated by Mukuro. Tsuna picked up the pocket watch and opened it, seeing a picture of First Generation Vongola Family with a young woman cuddled close to Demon behind the lid.
As Tsuna looks at the picture of the Primo Family, stating that there's a woman next to Demon. Reborn looks and says that he doesn't know who she is either as her face is unfamiliar. It's then Demon speaks and tells them that her name was Elena, his lover. He reveals his past with her and expressing how he thought the Vongola was the best Family at the time that they both loved more than anything else. However, this changed after Elena's death that caused by Giotto's careless decision to withdrew their military forces. For Elena's last wish, Demon promised to create the Vongola Family whose mere name will cause people to tremble, revealing that the reason behind all of his entire actions for years was all none other but for Elena's sake.
As Demon finished his story, Tsuna wonders if Elena truly loves the Vongola that way. This angered Demon, who questioned if he understood how Elena feels. Tsuna replied that he understands and thinks that Elena feels gratitude towards him and she knew that he never forgot her because he can feel it with his Hyper Intuition, and she would have thanked him. Hearing this, Demon tearfully asks for Elena's forgiveness for his inability to save her. As he fades away, Reborn states that it's now Tsuna's Vongola Family to lead and that there's no need for him to worry about the Vongola anymore since Demon himself should've realized from his own experience that despite having many weaknesses, Tsuna is not weak, assuring him the he can go back to Elena's side. Demon wonders how many decades have it been since he felt sleepy and listened to Elena's feelings. He comments on how the conflict has been resolved at last, even though it was following Tsuna's "awful script" (seeing through Tsuna's lie about his Hyper intuition). Finally coming into terms with his past, Demon accepts Tsuna and his Family as now he believed that he could entrust the Vongola to them. Before he fades away, he tells Tsuna not to bring shame to their name or he won't forgive him since it's the Vongola Family that Elena loved as he dies, finally able to rest in peace.