Second Lieutenant in the Imperial Japanese Navy. 21 years old. Speaks with a Satsuma regional drawl. His father is Rear Admiral Heiji Koito, Commander of the Ominato Naval District. His mother is Yuki Koito. His younger brother is Otonoshin Koito. He is characterized by thick inner eyebrows that resemble checkmarks, inherited from his mother. He also inherited his mother's fair complexion, leading his younger brother Otonoshin—who has their father's tanned skin—to tease him by calling him "Sakurajima Radish." Despite this, he is a kind older brother who never gets angry. His brother is 13 years younger than him. He dotes on his brother and talks about him often.