First we have Sousuke-sensei, who raised Taeko as if she were his daughter and then ended up marrying her. Taeko also ends up one after The Reveal.
Nicchi, who was a fairly harmless comic relief guy buy crossed straight to Jerk Ass territory when he helps Nozomi kidnap Kanau from Kouta and for being an overall ignorant jerk towards everybody's wellbeing. It doesn't help that he's also a Karma Houdini, since nobody calls him out for the above action.
Last but certainly not least, we have Nozomi, who kidnaps Kanau and her brother from their fathers without taking their feelings into account. Worst yet, she never loved Kouta from the beginning and used him to make Nicchi jealous (which backfired gloriously). She also did something similar to her soon-to-be husband as well. It doesn't help that she takes Kanau and tells the truth to Kouta in the jerkiest way possible.
The amount of sibling rivalry and parental favoritism that goes on without even a mention sometimes weirds out readers from different cultures.
Also, people from more individualistic cultures like America might have a hard time understanding why Kouta should have to give up on his crush just so Kanau can have her estranged parents back together. Of course, the Wham Episode makes the whole thing moot anyway.
The aforementioned openly pedophilic man used as a comic relief is something you'd never get away with in most of the western world.
The Woobie: The Nagato Family. they are The Faceless who just want to be noticed by the rest of Higansou. Kind of hard not to feel sorry for Them.