I love this manga so much ok. Kouta Hirano is amazing for creating this masterpiece. It literally has everything you could want in a dark manga. It has some humor here and there, the MC is OP but he's done right, the boss is a badass and isn't portrayed as weak just because she's human, the other main female MC gets some phenomenal character development (well actually a lot of characters do but hers stands out to me).
Hellsing