If there was no bdsm involved, Chuuya gets very lazy after sex bc he likes to bask in the afterglow and Dazai likes skin on skin so they cuddle together for a while before taking a bath together.
If it was a bdsm related scene I think they’d take aftercare very seriously, they’d have supplies ready before hand and personalize to each scene…Dazai likes being restrained so Chuuyas usually massaging them so they don’t stiffen up and I think Chuuya’s responsibility complex makes him feel selfish so Dazai let’s Chuuya take care of him but also helps Chuuya relax in subtle ways like praise and reassurance…I think Dazai would also get in his head but I’m getting way too off topic about skk and bdsm lol

They are excellent at taking care of eachother is my answer lol!