Kako is one of the Three Clock Keepers, a group that together forms the first of the Seven Mysteries of Kamome Academy. As his name suggests, Kako is the entity in charge of the past. He does not appear to have a real name of his own, and is called Kako by the human student Akane Aoi, who is contracted to serve the Clock Keepers.

In terms of appearance, Kako is depicted as a very old and unusual-looking supernatural being. He is notably tall and has a long beard, and he typically wears a hood that conceals his hair. He carries a staff, which is the tool he uses to manipulate time. Within the trio of Clock Keepers, Kako acts as a leader-like figure. His primary ability is the power to turn back time, which he wields using his staff. This power plays a crucial role in maintaining the flow of time within the school and is fundamental to his duty as the keeper of past events.

Kako’s role in the story is directly tied to the mystery of the Three Clock Keepers. This group, which also includes Mirai (the future) and Akane Aoi (the present), governs the flow of time at Kamome Academy. The narrative surrounding them reveals a critical plot point: when Mirai, who can advance a person's time, touches the protagonist Nene Yashiro, it is discovered that Nene has almost no time left to live. The Clock Keepers, including Kako, are instrumental in reverting time to undo this event, allowing the situation to be resolved without lasting consequences for Nene.

Key relationships for Kako are primarily with his fellow Clock Keepers. He is the leader of the trio, which includes Mirai and their human contractor, Akane Aoi. His development is not individual but is tied to the group's arc in the manga, where their combined power is necessary to reverse a fatal outcome for one of the main characters. His notable ability, as the keeper of the past, is the power to reverse time, a skill that distinguishes him from his partner Mirai, who manipulates the future.