Nyau is one of the three members of Esdeath's personal guard unit, The Three Beasts. While he comes across as easygoing and harmless at first glance, he's actually the most twisted of the group—his hobby is collecting human faces, which kind of says it all about his actual personality.
Like his fellow bodyguards, Esdeath had him hunting down Night Raid operatives while quietly eliminating her political rivals. He got his big fight scene against Tatsumi and Bulat on the luxury cruise ship Ryuusen, where he used his Teigu weapon, Scream, to knock out everyone aboard. The ability itself puts people to sleep, making him a pretty dangerous opponent even if his methods seem cartoonishly creepy.
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