In the late 1960's, Fukubei snuck into the secret base which Kenji and his friends created to read their Prophecy Book. While there, he ran into the masked boy SadaKiyo, who was also sneaking in. Sadakiyo asked Fukubei to be his friend. Fukubei agreed, but told Sadakiyo never to refer to him by his real name, but to call him "Friend" instead. This is the first known use of the title by Fukubei.
Fukubei would go on to form a group that consisted of himself, Sadakiyo, Yamane, and Katsumata. The four of them, after reading The Prophecy Book created by Kenji and his friends, decided to create what they believed to be a better version entitled The New Prophecy Book.
As an adult, he developed his Friend persona into a charismatic cult leader. Taking advantage of what he saw as people's desire for a saviour, he used magic tricks (such as making himself appear to float in midair) to make people believe he was a supernatural being that had come bearing salvation. In the 1990's, he seduced Kiriko Endo so he could manipulate her into developing a virus that would destroy humanity and a vaccine for it. Kiriko
also gave birth to Fukubei's daughter, Kanna Endo, who lived with her brother Kenji in her early childhood years. Katsumata would later confirm that he and Fukubei had somehow successfully experimented on Kanna in the womb, imbuing her with special abilities. Considering Fukubei's constant lying and use of tricks, it is likely that Kanna's powers were an attempt to reproduce and build on Katsumata's precognitive abilities, rather than an original discovery by him.
Fukubei was shot and killed in the science room at his former school by Yamane in the early morning of 1 January, 2015. His death was confirmed by Otcho, and later by Manjoume. Shortly afterward, Katsumata took Fukubei's place as the second Friend by posing as Friend's body lying in state, only to stage a phony "resurrection" later on.
Considering Fukubei's unexpected death, and that Katsumata wrote the last sections of the New Book of Prophecy, it is unclear what Fukubei's own plans would have been had he survived.
Fukubei bears a resemblance to Johan Liebert, the main villain of Urasawa's preceding manga Monster. Their hairstyles and empty eyes, as well as their roles as main antagonists and abilities to influence the people around them, are similar. Also, given Urasawa's artistic ability to distinctly depict characters of different ethnic groups, Fukubei could be considered a render of Johan as a Japanese man.