Leon Greyrat: The Second Son - Mushoku Tensei OC

One day in the six-faced world, a newborn child, completely conscious of his surroundings, is taken in by a certain party of adventurers... the Fangs of the Black Wolf.

But not two years later, the party splits, and our main character, Leon, is greeted with the pleasant surprise of a younger brother, in the form of Rudeus Greyrat.

As Leon discovers more of the world and increases his strength to stave off any danger he could encounter, he comes to realize that in this world, and in his life, there is one thing he holds dear above all... family.