However, things change when Eiji becomes a host to half of a set of purple Core Medals that react to his lack of selfish desires, the same presumed reason why he is able to use Kamen Rider OOO's powers without any sign of going berserk so far, with dangerous consequences. In the process, joined by Akira Date, Eiji learns more of the Greeed's desire to become whole and the reason why Ankh is unable to assume his complete form when Ankh(Lost) appears. Soon after facing the Greeed Kazari that Eiji is approached by the Kougami Foundation, and is offered a partnership with them in the fight against the Greeed. Feeling guilty for getting Shingo involved, Eiji remains by Ankh's side as the two are joined by Shingo's little sister Hina Izumi. However, after the Greeed take the half dead body of Shingo Izumi for his own, Eiji manages to force Ankh into promising him that he can transform to save lives, not just to gather Cell Medals. After destroying the Yummy, Eiji learns more about the Greeed and Medals from Ankh, who originally intends for Eiji to be a tool for gathering Cell Medals for him.
When Eiji risks his life to rescue him, Ankh gives him two more Core Medals and the OOO Driver as means to transform into Kamen Rider OOO. However, when attacked by a Yummy, the arm reveals himself as Ankh of the ancient beings known as the Greeed, and the red coin is one of his Core Medals. This causes a disembodied arm to begin to follow him around, demanding the red coin from him which is actually a part of his being. Returning to Japan to allegedly fund more of his world travels, Eiji's latest part-time job at the Kougami Art Museum ends due to the destruction of the museum around him while in a drugged slumber, taking a strange red coin he found as his supposed pay. Eiji's rationale for helping people is if someone reaches their hand out to him and he does not reach back, he will regret it for the rest of his life. He became willing to help those in need, often going so far as to risk his life for complete strangers. Though the Hino family used his sob story to get the people's support, the ordeal peculiarly caused Eiji to lose all selfish desires, resulting him being a vagabond with no permanent job, no home, almost penniless and no life. However, his money was used to fund a civil war that cost the life of a little girl Eiji befriended, whose death he was unable stop, forced to looked on helplessly. While in Africa a year prior to the beginning of the series, Eiji attempted to use his fortune to help out a small village. Eiji is the son of a politician who travels the world with his grandfather, thus growing up in a lavish environment.