All three of them like each other. Mizuki likes Fujiwara and Takeru; Fujiwara likes Takeru and Mizuki; and Takeru likes Mizuki and -- this is the only one that's not really as strong, but he's a boy with high libido and she's a hot girl so it seems fairly resolvable -- Fujiwara.
It's so symmetric too: boy, girl, and androgynous Eldritch abomination cursed by the Norse Gods.
(What gender would he turn out if s/he chose both of them? Both dick and pussy? Neither? Even if s/he has to pick one or the other, Fujiwara and Takeru both seem okay with either.
For that matter, what does Sugito Akira have against homosexuality? Frankly, all else being equal, I'd prefer being a man and not having to deal with periods and the like. There's still the prostate gland.)
Polyamorists would kill to have a relationship so already jealousy free. Maybe it's the
yamato-damashī, but they were already so selfless in giving up their own crushes to support each other's.