(oh thank you! you’re more hella tbh v u v)
Makoto: He might just call them by a shortened version of their first name, and always add a “-chan” if they were a girl or especially cute at the time.
Haruka: Haru doesn’t really address anyone too lovingly, so he just uses their first name or maybe embarrassingly try adding a “-chan” to a girl’s. (Very rarely, though.)
Rei: He always politely adds a “-san” onto their first name to show that he respects them, but he’d blush if he tried to address them without any honorifics.
Nagisa: As expected he adds his trademark “-chan” nickname onto their first name, but when he’s especially happy he’ll tag on a cheesy “honey” or “dear”.
Rin: He finds it way too embarrassing to give them a cutesy pet name, so he just chooses to call them by their first. But if they’re acting overdramatic or bratty he’d sarcastically call them “princess”.
Sousuke: He doesn’t exactly get the point of pet names, but he thinks they’re kinda funny. When he gets the chance he teases them by calling them “love” or “my everything” to get them flustered.
Nitori: He’d also get too embarrassed to call his partner by anything too weird, so maybe he’d start with something sweet, like “sunshine”.
Seijuurou: Normally it’s just their first name, but he goes all-out and has way too much fun embarrassing them with the most embarrassing pet names: Juliet, sweetie, Honey Bunny, everything.
Momotarou: He thought it’d be cute to start giving his partner a pet name, so he’d probably give them something cheesy like Peachy Pie in public, which would result in him getting hit for saying it so shamelessly.