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.
Mitsuhide follows Zen and spots him chatting with Atri. While observing Atri doing manual labor, Mitsuhide notes malice in his eyes and becomes suspicious. He reports this to Izana. Atri tells Zen his work is changing to the night shift and asks Zen if he can sneak out at night. Zen sneaks out that very night to meet Atri only to find him wounded. It is revealed that Atri is part of a gang, whose members are bitter and murderous towards Izana for ruining the Lido family and plan to take Zen hostage. They wound Atri to ensure he doesn't change his mind at the last minute and protect Zen. Izana and Mitsuhide arrive to confront and fight the traitorous gang. Zen is forced to defend himself from Atri ready to loose his arrow at him. Atri tells Zen he is merely settling a grudge and that despite being the same age, Zen having everything while he has nothing, is ridiculous.
Zen blocks an arrow but wavers at attacking his former friend. Atri readies another arrow but Mitsuhide steps in between them and deals the killing blow. Atri dies, still believing, "It would have been better if you weren't a prince.."
Though Atri never considered Zen a friend, Zen still grieves for him and keeps an arrowhead from one of his arrows as a memento of that time.
