Mutsuki's girlfriend Nozomi provided a significant amount of help as well. Although she couldn't assist with fully suppressing the Spider Undead's power, her love for Mutsuki enabled him to at least partially resist the mind control. Mutsuki was able to figure out that Kamen Rider Chalice is really the 53rd Undead: Joker Undead and that he will become the strongest enemy when the rest of the Undead are sealed. He says to Garren that he will defeat him before that happens. Mutsuki at one time had all of Kamen Rider Chalice's sealed cards because of the Category King Cacacus Undead. He tells Mutsuki that he should stop caring for his girlfriend if he really wanted to become stronger. He continued being controlled by the darkness of the Category Ace until he sealed the Tiger Undead, who now encourages him to fight only for the sake of others. Eventually, when Kenzaki is not able to defeat Joker/Hajime, Mutsuki decided that it was he who would seal the Joker. He battled Joker with all his might and despite that, he lost the battle. He was last seen with his girlfriend playing some basketball.
In the Missing Ace movie, after Joker/Hajime was sealed, four years have passed and Mutsuki has tried to forget about being a Kamen Rider, working to have a normal life again. This was abruptly put aside when he witnesses the Category Ace of Clubs and was compelled to transform into Kamen Rider Leangle. Together with Kenzaki, Tachibana, Kotaro, and Shiori, they figure out that Glaive is really the Joker that everyone is looking for. But he still manages to take the ancient power and use it on the Riders. But thanks to Hajime's sacrifice, he, Blade, and Garren were able to defeat the Albino Joker and save the world once again.