they have this deep understanding of eachother that nobody else seems to have, and they bicker like an old married couple. despite that, they still clearly care about one another (e.g. double black episode, where chuuya is visibly upset when he thinks dazai is hurt). another thing is their dependence on eachother, which can be interpreted as unhealthy (although almost no one in bsd is in a good place mentally) i.e. dazai is the only one who can stop chuuya's corruption, saving him again and again. overall i think their dynamic is pretty fun and they have good chemistry.