Kage is a last surviving member of the Shadow clan and Bojji's loyal friend and protector.

Years of uncertainty and abuse led him to develop a very rough exterior, pretending to be a hard-bitten thief, when in reality, Kage is empathetic and kind-hearted.
After meeting Bojji, he was touched by his kindness and circumstances, then dropping his pretense around him, pledging to be his faithful friend.

Kage is much more worldly and savvy than Bojji, and tends to act as both the voice of reason and resident skeptic on their adventures.

(Source: Ousama Ranking Wiki)