Akuninmenshita B-kyuu Boukensha: Shujinkou to Sono Osananajimitachi no Papa ni Naru

Gray, the B-rank adventurer, was a background character in the RPG known as Bright Fantasy …or at least that’s what he thought. After saving orphans from being attacked by goons, he resolves to provide for them as a father. But one of the orphans is Iska, the other world’s future hero, and his choice will greatly change its destiny.
(Source: One Peace Books)