Scrounger: My sister became stronger by leeching from me.

In a land beyond yonder, lay two twins. Both without their memories, they survived from hand to mouth. Or even worse, hand to the floor. Yet one fortuitous(?) encounter with a cowardly demon lord and their life starts changing upside down as forces beyond their scope of mind slowly start emerging in the world. How will a boy who looks like a girl, a parasite sister who can only leech after her brother, and a butler who's actually a demon king survive in this world?