Oooh, No Longer Human, one of my favourite japanese novels so far, fantastic! I’ve read it in English before, it was always my goal to read the original eventually. I wished they had translated the title more literally, “Disqualified from being Human” (or “as a human being”), which is such a fitting title, but i guess it’s a bit unwieldy in English. I didn’t know that this novel is referenced so much in Japanese media though!
I think i first heard about this in the anime series 青い文学 as well, a compilation of short anime adaptations of classic literature, which i also recommend, it’s a great introduction. Like much of the modern classics it’s not the happiest, but as the motto of the series says,
(where 青い apparently also/primarily means “evergreen”? But blue also fits)
Interestingly, the series also adapts a short story by Osamu Dazai, 走れメロス (Run Melos!), inspired by greek mythology, which is very uplifting. But the entire series starts with No Longer Human, which is apparently the most widely read novel in Japan.
I’m not sure if i’m ready for this, as my grammar is just around N4-N3 (according to Bunpro), but i think i want and have to at least try the beginning to celebrate one of my favourites 
(the other favourite (author) being Soseki, naturally, whose Sanshiro trilogy has a lot of thematic similarities to No Longer Human. こころ as well, come to think of it.)