Simone tends to go with dear or simply his lover’s name, occasionally using a title when he’s teasing someone (such as a goddess or a certain prince, who gets called His Imperial Excellency when Simone is giving him lip). He has a platonic love affair with a woman who he sometimes addresses as Milady, if he isn’t addressing her with the proper title of her church.
Quinn goes with sunshine, which is honestly really uncreative, seeing that his boyfriend is empowered by the sun.
Shiko prefers names as well, but two specific people, both mentors to her, are addressed as Sensei and Sifu, due to the titles given in her native culture and in the community she now works in. She’s going to eventually start calling her primary SO Kitten, as he is a celestial lion.
Fluttering Ash Cicerone referred to her spouse as Dear Heart often.
Justin would go with dame, dollface, or ‘the crazy broad who puts up with him’ outside of his girlfriend’s earshot. Yes, he’s one hell of a catch, but he knows you have to be insane to deal with him and his other half, the ghost of a 1920s bootlegger.
Yuuki would call Noriko a rutting bitch at times, but only in private, with her consent, as he’d rather not let anyone know she is the child of a dog spirit, and she puts up with it because watching his prim, proper mouth work up the nerve to say such vulgarity was funny to her.
Sereno refers to Ulciscor as his gentleman friend, feeling that boyfriend doesn’t suit him, and has given him the pet name cielo, as to him, the damn mage is his heaven.
Kim Cheolsu probably would go with non-verbal endearments, as he’s a dork who would rather smile and wave or reach out instead of really talking too much, I think. And words are hard for him.
Fu has a habit of calling his girlfriend (now wife) Princess with as much sarcasm as he can muster just to piss her off. The two have a masochism tango going on, but it has been very much discussed and understood where to draw the lines.