Mamoru is a quest-exclusive NPC that appears in the Taurus Iracundus Chapter, Act I: Rise Up, Golden Soul.
He first appeared in Character Teaser - "Arataki Itto: That's How the Show Should Go!"alongside fellow Arataki Gang members Akira and Genta.

https://genshin-impact.fandom.com/wiki/Mamoru
mamoru (genshin impact)