Stigmata - Rain and Thunder

All Tatsumiya Renji has ever wanted is to find his missing sister. When a chance encounter finally pits him against what looks exactly like her, however, he falls under her hands. As he wakes up from the shock, he's already found himself in a desert-like world, and worst of all, he's also slowly turning into a monstrous figure! Will Renji be able to navigate through this strange new world where friends and foes alike await and find his sister, or will he succumb to the monster that's slowly eating him from the inside?