Well, while the writing isn't really stellar I thought Takeru's (the protagonist) character progression was mildly interesting, in the first tetralogy he is barely a character, just a meek NTR bait who is pitifuly nave, oblivious to his surroundings, little presence, only a few lines of dialogue, but by the final game he has grown into more of a character somewhat, his breakdown once he finds out about everything is the high point in the series in my opinion, dude was really losing his mind.
I wonder if Nomad will keep beating this dead horse in the future, since the ending is sort of open - it is strongly implied (I'm being very kind here, it's basically confirmed) Haruka went back to cheating even after they had a bittersweet talk were they pin for a second chance, while Takeru chants a madness mantra: everything is fine, everything is fine, everything is fine, everything is fine in order to calm down and try deny in his mind the loud moanings coming from his father's room.
Takeru would probably end up killing himself, or his father, or his wife, or just everyone in the shithole that is his life if this shit went on and his character kept getting new shades.