Gleipnir 11

Dark, disturbing, and sexy, this sci-fi action manga that inspired the new anime stars a dominating teenage girl searching for a sister who became a monster, and a submissive boy with the strange power to turn into a ragged but powerful beast, with a zipper down his back and a compartment on the inside just big enough to hold a human body.
A DUEL TO THE DEATH Shuichi and Claire thought they were preparing to take the fight to Kaito, but instead, he brought it to them. His minions stormed the school, massacring innocent students. To save their friends, and possibly the entire world, Shuichi and Claire have no choice but to kill the boy who collected one hundred coins. But will their incredible new fusion be enough?