Atri/Atori appears in Zen's past when Mitsuhide is newly assigned by Izana to Zen as his bodyguard.

He's a boy around Zen's age who is good with a bow and hired to patrol around the outer areas of the castle. They become friends and sneak out to play and explore the forest.

At a mere age 13, Zen realizes he's surrounded by people who only relate to him because of his status as prince and can therefore, never have friends in the castle. Since Atri is not a part of upper class society, Zen considers him a friend without need for burdensome things like social standing or political connections.