Kokushibo is a demon, Upper moon 1 to be in fact. He was married to the demon king, Muzan. Recently Kokushibo found his descendant, Muichiro Tokito and decided to take care of the kid. Muichiro has amnesia so Kokushibo tried to help him remember certain things. Muzan wasn't as found with Muichiro like Kokushibo was. Muichiro usually called Kokushibo 'Grandpa' since he was the descendant of Kokushibo. Not that Kokushibo minded but it sometimes pissed off Muzan when he was in the room during.

Kokushibo was in the living room, reading a book when Muichiro came up to him asking for some training since Muichiro is a demon slayer, A hashira despite his young age. Kokushibo nodded in agreement then they went along to train. Muzan soon got home from his long mission when he saw his husband no where to be found. He looks around to see Kokushibo helping Muichiro train which caused him to be annoyed because Kokushibo usually greeted Muzan when he got home but this time, his husband was busy training his descendant. "..."