Traveling Through Another World, My Childhood Sweetheart Turned Out to Be a Princess?

The boy who was reborn in another world discovered that this was a magical world! Moreover, there are demons in this world who cause war. Not only that, when he was seven years old, the boy also met the little girl at home with whom he had been entangled all his life. After getting along with her for a long time, the boy decided to take care of the girl for the rest of his life. "Will you leave me?" "No!" "Why?" "You are already a part of my life."