These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Badass Decay: Tokiya in the latter arcs of the manga, giving up his need for Revenge robbed him of several of his competence, notably failing for a trap so obvious that Domon, someone much less intelligent figures out right away.
Moral Event Horizon: While in-verse he crosses it, when he gloats on Hisui's death on a crying Fuuko after admitting he staged Hisui's murder of her lover. Out-verse, he crosses it when he kills Kurei's lover and his adopted daughter, Kurenai, just to anger him.
Mokuren crosses several times (his beating of Recca's teacher's wife, gloating over Yanagi's suffering and backstabbing Kogenai), but finalizes it with his murder of Mikoto, his lover, for proving to be useless.
Kadotsu crosses it when he admits to slaughtering Team Ku easily.
Real Women Don't Wear Dresses: One of the main reasons why Yanagi is The Scrappy in some circles is because she is never an offensive Action Girl. She did have some backbone and does help out at times in the manga (even if she doesn't fight). However, since the anime seemed to remove that backbone...