Atri appears early in Zen's story, showing up right around the time Mitsuhide gets assigned as his bodyguard by Izana. He's roughly Zen's age and works as a castle archer, patrolling the outer grounds—basically the kind of person Zen would never normally interact with given the whole prince thing.
The two hit it off and start sneaking out together to mess around in the forest. It's a pretty big deal for Zen, actually. By age 13, he's already figured out that everyone around him only cares because he's a prince. It's a lonely realization—he can't really have genuine friends when everyone's thinking about status and politics. Atri, though, doesn't come from that world. He's just a kid who knows how to shoot a bow, which means Zen can actually be friends with him without all the baggage that comes with court life.
Content compiled by AnimeList.moe from publicly available sources.
