Guyver: The Bioboosted Armor

The Tragic Enzyme II (1x13)

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After escaping with Mizuki and his father, Sho discovers that Mr. Fukamachi had been altered by Cronos and he becomes a powerful Zoanoid named Enzyme II, Sho fights with him, but half heartedly as he does not wish to kill his father, until a brutal attack destroys Sho's brain. The Guyver then stands, fighting on its own while Sho is too critically injured to fight. The robotic systems, immune to Sho's human emotion kills Enzyme, much to the horror of Tetsuro and Mizuki.