@Cheatplayer It's not well explained in the manga, but in the novel, it's hinted from the beginning that he's not exactly at the state he was at after 100 million years. His body is still the same from the time before he pressed the button, and now he is still adapting and training his body to match the training he did in that world. In the future, it's shown that
his 100 million years self actually existed inside him as a separate unhinged entity, and the current normal him is due to him trying to repress the madness from practicing for 100 million years. When he is in grave danger or unable to control his emotion he might turn crazy and simply wanted to fights/kills anyone around him.