Mogami has only be shown asleep, so nothing is known of his personality.
Mogami is swaddled in a white cloth. He has a small tuft of light colored hair growing from his head.
Mogami is brought along when Kikaijima reunites with her friends on the tenth anniversary of Ajimu's disappearance. He is handed to Zenkichi Hitoyoshi by Kikaijima, who expresses her desire for Mogami to grow up to have a strong will like Zenkichi. She explains his name means "best", to signify that he is her most important treasure. At some point, Kikaijima takes Mogami back from Zenkichi. A flustered Youka Naze holds Mogami as Kikaijima watches.
- Mogami's name means "the best" (最上の, saijou no). Mogami is an alternate pronunciation of saijou.
- The first two kana of Mogami's name come from Mogana.