Girochin no Tsume

From Blackbox: Working in an oppressive environment is not always easy. Especially when, in spite of being a teacher, you lack strength of character. Keisuke Nachi is worried by nature. But one day, he finds himself equipped with claws capable of slicing through the hardest metal. Perhaps a consequence of his medication? A strange young man appears then and puts forward a theory for him.. For Keisuke, all this means only one thing: it is time to take his revenge on the world.