My favorite topic!!!

From like a day-to-day, typical sex routine kind of answer, I think they have a few favorite things in rotation: jerking each other off in the shower and/or thigh-fucking in the shower, Atsumu giving blow jobs, edging (probably competitively lmao, always daring each other to try and last longer or one up each other), and Atsumu fingering Kiyoomi until he’s a moaning, fucked out mess begging for more.

(Side note, I really like to imagine they don’t make out that often b/c Kiyoomi isn’t that into it until he occasionally just gets in the mood for it, and then they make out/grind until Atsumu comes in his pants because he loves it and doesn’t get to enjoy it all that often.)

As for thoughts on what they like to experiment with and explore when they have more free time. I’m sure this happens here and there but especially during their breaks when they don’t have to worry as much about leaving marks/being sore… so in that realm, I’m always a sucker for spanking/choking and I think they definitely fit those vibes. I loooooove thinking about size queen Kiyoomi in the off-season whose number one goal is to someday take Atsumu + a dildo at the same time.

I also like the idea of Atsumu who has some voyeuristic tendencies and really wants to be watched (but in more of a fantasy way then a reality way), so he likes taking nudes/filming videos of himself and sending them to Kiyoomi who, in turn, threatens to post them online if Atsumu doesn’t keep the apartment clean enough.

I could go on forever. OP - did you want this answer in a 5,000 word essay or 50,000 essay, I forgot to ask????