Demon arrives from the Vindice Prison after possessing Mukuro's body. When Tsuna and the others are about to attack, Chrome stops them from doing so, since it would damage Mukuro's body; however, Mukuro states that if they don't fight with everything they have, they would lose everything. Convinced, Tsuna and the others assume their battle position.
Kyoya Hibari vs Demon Spade Edit
As the battle begins, Demon sent Gokudera, Yamamoto, Lambo, and Julie to his illusionary universes, leaving Tsuna, Enma, Chrome, and Hibari (aside from Reborn and Mukuro in owl form) to fight him. Hibari challenges Demon to a one-on-one battle and tells Tsuna and the others to stay away. Tsuna hesitates but Reborn convinces him that Hibari has let Tsuna fought Enma while he's watching. Demon is amused by this and comments that Hibari is just like Alaudi. Hibari directly attacks Demon but Demon uses Kouyou's Forest Flame to counter it and then uses Shitt P!'s Swamp Flame to suck Hibari into a swamp by using the Simon Guardians Rings that he stole from Vindice Prison. However, Hibari manages to get away and once again attacks Demon, but his attacks are block by Demon who's using the same Cloud Vongola Gear as Hibari did, surprising everyone present.
Demon reveals that he could also use Roll and Reverse Needle Sphere as Hibari does. Making the others wonder how, to which Demon answers it's because it was his attribute, but Mukuro counters and answers it's Mist. He reveals the same Earrings of the Mist that Chrome possesses, leaving Reborn to come to the conclusion that the Vongola Gears are illusions. Knowing it's fake, Hibari confidently attacks again and seemingly gains the advantage as he continues his barrage on Demon. But Demon turns out to be using the Sun Vongola Gear and uses Maximum Sunshine Counter on Hibari. Hibari was able to dodge, but Demon revealed that he missed Hibari on purpose and traps Hibari into his illusionary world.
Tsuna turns into Hyper Dying Will Mode and flies straight to Demon who uses Storm and Lightning Vongola Gears to attacks, catching Tsuna within explosion. But then Enma enters the battle as he says to Tsuna to beat Demon together.
Tsunayoshi Sawada & Enma Kozato vs Demon Spade Edit
After Demon reveals the truth behind the Flood of Blood incident, Tsuna and Enma fly to Demon out of rage as Demon uses Rain Vongola Gear to attacks. Tsuna and Enma manage to dodge the attack. Demon then summons Blizzaroids to hinder them but Enma unleashes his Gravita Della Terra to suck up the Blizzaroids with its Gravity. Tsuna commands Nuts to Cambio Forma and uses X-Cannon on Demon. Demon dodges the shots but with Enma's Gravity, the blasts turn around and hits Demon.
However, Demon survives by using Sistema C.A.I and decides to get serious. He activate all Vongola Gears and Simon Rings, enabling him to use all Six Flames of the Sky and Six Flames of the Earth in addition to multiplying himself into six. The six Demons attack both Tsuna and Enma, separating them to prevent them from coordinating their attacks.When Tsuna lands a kicks on one of the Demons, that Demon turned into illusions. Mukuro explains that Demon has masterfully woven his illusions into the fight and that only highly skilled illusionists can see through such advanced techniques. Chrome intends to assist Tsuna and Enma but another two Demons stop her and threatens to kill them if they interfere.
As the battle continues, Tsuna is able to inflict damage to one of the Demons, but the damage is reduced to 1/6 of the original power unless he could attack all of them at once. Hearing this, Enma sucks all six Demon with his black holes and gathers them around him as he tells Tsuna to incinerate Demon and himself with all of his Flames. Tsuna refuses to kill Enma along with Demon as he's terrified of sacrificing a dear friend for victory, until Chrome jumps to Enma's side and creates a Mist Barrier supported by Mukuro to protect Enma from Tsuna's attack. Convinced that Enma will be safe from his attack, Tsuna blasts his XX-Burner at full power toward Demon.
Tsunayoshi Sawada vs Demon Spade Edit
It turns out, Demon was able to survive from the devastating XX-Burner and retaliates by crushing Tsuna's entire bones. Reborn intends to help him but the Vindice prevent him from doing so because there's a hidden reason for them to stop him, an act that deeply angered Reborn. While Tsuna lies on the ground helplessly, Demon prepares to deliver the finishing blow when all of a sudden Enma's Simon Ring flies off and combines with Tsuna's Vongola Ring, giving Tsuna a new power to fight. The combined rings ignite the Flame of Oath that heals Tsuna's shattered bones with the Earth Flame's Gravity coating. The Vindice reveal that the rings are also left by Giotto and Cozzato, thus, revealing the Seventh and last Key of Giotto and Cozzato's memories. After the last key was shown, Tsuna immediately overpowers Demon and critically injures him with X-Burner.
Refusing to lose, Demon claims that he will use his trump card. Tsuna comments that he's pitiful because his trump card will be the Eighth Element Flame that he would use to run away. Demon reveals it's true and mentions about the Eight attribute, making the Vindice tells him to shut up or they will interfere. Demon opens the portal but Tsuna stops him with Earth Flame's Gravity Manipulation. Tsuna takes his stance and is about to finish Demon with his X-Burner, but then changes his mind and tells Demon to surrender and atone for his sins, angering Demon even further.
In a moment of desperation, Demon decides against using his trump card and surrounds himself with the Eighth Element Flames, choosing to face Tsuna head-on using all of his flames. Both Tsuna and Demon prepare for the ultimate clash that determines the fate of this battle. In the middle of it, however, Demon abandons Mukuro's body, causing a distraction that allows him to escape using the Eighth Flame portal. However, the Vindice destroys the portal stating that only ones with a physical body could use the Eighth attribute, thus leaving Demon defenseless and giving Tsuna the opportunity to finish him.
Tsuna blasts his X-Burner one last time at Demon Spade's soul, directly hitting him. As Demon Spade's soul stumbles onto the ground, something fell from Demon Spade's body, which turns out to be a pocketwatch and Demon Spade's treasure. Tsuna picks the pocketwatch and sees an old photograph of the first generation Guardians with a woman beside Demon.
Tsuna reveals what's inside the pocketwatch and Reborn wonders who's the woman next to Demon since he had never seen her before. Demon, who's dying, answers that the woman is Elena, his lover. Demon reveals his past with her and how they worked together with the Vongola to protect the weak. However, when Giotto disbanded his military forces, their territory was left vulnerable to an enemy attack that led to Elena's death. This event triggered him to swore to make the Vongola the strongest Mafia Famiglia.
After hearing his story, Tsuna wonders if Elena truly loved the Vongola that way, angering Demon who then questions if Tsuna understands Elena's feelings. Seeing Demon Spade's condition, Tsuna replies that he understands because of his Hyper Intuition and says that Elena feels grateful towards him and she would say thank you. As Demon looks at the pocketwatch, he tearfully pleads for Elena's forgiveness for failing to save her back then. Demon starts to fades away quicker, at this time Reborn tells Demon that he had lived far too long and now he can relax and go back to Elena's side. Reborn convinces him that he could leave the Vongola to Tsuna since Tsuna's not so weak that he would need to worry. Demon finally accepts Tsuna and his Guardians, leaving the Vongola in their hands as he dies, finally finding peace.
The trapped Guardians in Demon Spade's illusions and the imprisoned Simon Guardians along with Ryohei are freed and reunited with everyone, as each one of them reconciles. Meanwhile, Mukuro returns to his own body; however, they are then interrupted by the Vindice, who have one last thing to tell them.