Mukuro Rokudo vs. Demon Spade is the ninth major battle of Inheritance Ceremony Arc.
Demon removes the barrier of Simon Island and Chrome's illusionary organs to taunt Mukuro to come out or Chrome will die. Mukuro immediately replaces Chrome and claimed that he will drag Demon to hell. After witnessing the sixth key, Mukuro and Demon briefly clashes their weapons until Demon brings out his deck of cards.
Mukuro mocks Demon Spade's cards, saying that it's simple and useless, to which Demon takes as compliment and warns him that its not a normal set of cards. He reveals that since he possesses the Mist Flame of the Sky and the Desert Flame of the Earth, Mukuro won't be able to win with his current power. However, Mukuro is not fazed by this and brings out the ore of Mist Vongola Gear that was left by Chrome. He upgrades it to the Earrings of the Mist Version X and goes into Cambio Forma, which changed his trident into a Khakkara. Mukuro begins to use his illusions, trapping Demon within it.
Mukuro creates an illusion of himself turned into a giant and crushes Demon who then stumbles on a lotus flower. Mukuro is about to kill him but stops when Demon changes himself into Chrome with his own illusions. The eyes of Mukuro's illusions change into Demon Spade's cards and summon illusions of Fran, Ken, Chikusa, and M.M. Demon use these illusions to attack Mukuro, thinking that they would make Mukuro's concentration dull because they are his comrades that he shares emotional bonds with. When Demon who's disguised as Chrome attacks Mukuro, Mukuro unexpectedly impales all of the illusions with his Kakkhara.
Mukuro states that he doesn't consider them as people whom he shares emotional bonds with but they're himself. While reverting to his original appearance, Demon questions Mukuro about what he meant and why he seems angered when Chrome's being used. Mukuro replies because he doesn't like being controlled. Demon realizes that Mukuro's bonds with his allies are absolute unity as he comments that they're outrageous before losing consciousness.
Despite being defeated, Demon,instead, is grateful to Mukuro but soon becomes unconscious. Tsuna and the others arrives at the place and are surprised to see Mukuro already defeated Demon. Mukuro changes back to Chrome as he's already exhausted. Everyone thinks that the battle is finally over until Mukuro, now possessing Mukurou, reveals that he cannot return to his own body because he was blocked. Julie awakes wth no memories of the commotions that occurred. Tsuna and the other think that Demon is still possessing him but Chrome and Mukuro interject that he's no longer Demon. Piecing everything together, Mukuro reaches the conclusion that while he's possessing Chrome's body, Demon used the opportunity to take over his soulless body in Vindice Prison.
This shocks everyone as Mukuro finally realizes that Demon lost on purpose so he could possess his body in Vindice Prison with the power of the awakened Simon Ring. Then Vindice appears before them, making Enma thinks that they intend to take Julie and him since they have lost. However, the Vindice reveals that Demon who currently possesses Mukuro's body has escaped from the water prison and it won't be long until a jailbreak occurs. The Vindice says that Demon from long ago until now is part of Vongola, and thus, Tsuna and the others must take responsibility for it. Tsuna agrees but, in return, the Vindice must negate the battle between Vongola and Simon and free the imprisoned family members if they able to defeat Demon. The Vindice promises this and reassures Tsuna and the rest that they won't go back on their own words as one reveals himself to be Bermuda, the one who witnessed Giotto and Cozzato's oath.
Before they could question Bermuda any further, a flash of power arrives at the island, causing massive destructions to their surroundings. Gokudera and Yamamoto protect the rest with their Vongola Gears, fully draining their remaining flames in the process. Once the flash of power disappeared, a black portal appears followed by Demon Spade's signature laugh. The Vindice comments that Demon has finally gained their attribute. Demon steps out of the portal while claiming that it's time to end Tsuna's generation.