That's two diffrent kinds of trauma clashing. For Uke there's internal issues like self acceptance, low self-esteem, lacking social interation. For Seme there's external issues, mother abandonment, feelings of being rejected by people he loved (like Uke), loneliness for having to leave his comfort zone (his dog, his former school). Ordinary Yaoi plot, but Yeah! this wouldn't have been a story without the lack of communication (as usual) that yaoi manga posses.
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About character development, "Kiyou" especially changed a lot, Compared to how he was like as a kid, and then now when he adopted this "I'm the root of all evil" attitude. it was a change for the worse, but he definitely wouldn't act like he did at the end if he didn't accept the worse truth to be abnormal generously. "Tsurugi" changed too, his abrupt moving warped his mind. Altough he didn't change much since reuniting with Kiyou, he just became more desperate as his tactics didn't work and his actions escalated.
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From my perspectives, characters development is basic and storyline goes with monotonous regularity
Doushiyoumonai Renjo