I Transmigrated to Another World, and My Childhood Friend Is Actually a Princess?

A boy reborn in another world discovers that it's a world where magic exists!

And this world also has a demon race that sparks wars.

But that's not all. When the boy is seven, he meets a little girl at home who will remain entwined with him for the rest of his life. After spending more and more time together, the boy makes a decision: he'll take care of her for the rest of his life.

“Will you leave me?”

“No!”

“Why not?”

“Because you're already a part of my life.”