Read Sword Sheath’s Child manga
Bira is a kid who loves fishing, living and wandering in the wilderness with his dwarf grandfather. One day, his grandfather tells Bira to wait for him at the Northern part of the forest and disappears. Bira waits for many years living in forest while befriending a family of bears and staying away from humans, just as his grandfather had warned him to do. By chance, he meets and saves Tanyu’s life and later becomes friends with him. Upon hearing his friend going on a dangerous mission, Bira leaves the forest for the world outside to save his Tanyu.