|Manga debut||Yu-Gi-Oh! ZEXAL Rank 35: "Separation!!"|
During his Duel with Shark, when the latter asked Kyoji what caused him to fall that far, joking that it could have been hell, Kyoji answered that indeed it was hell - his little brother had died by his own hand.
Kyoji then revealed that they were an average happy family, but five years prior to the Numbers War, Kyoji and Yuji's parents died in an airplane crash. Kyoji ended up in a facility, while Yuji was sent to a foster home.
Wanting to meet Yuji again, Kyoji decided to become Duel Champion, so that Yuji would eventually see him again. One year prior to the Numbers War, Kyoji had become Far East Duel Champion. Then, six months prior to the Numbers War, he received an e-mail on his D-Pad from his brother, Yuji, and the brothers finally were able to meet each other once more.
However, Kyoji later discovered that the real Yuji was abandoned by his foster parents and choked to death by a delinquent orphan so that the latter could replace Yuji and make money off of Kyoji's success.