Something that I struggle with that I also keep running into in fic is that Taion...  really just has a kind of a flat affect! He just is kinda stone-faced, having far more in common with the various kuuderes and emotionless girls than any particular defrosting ice king tsundere genius character from other media. I’ve joked about how Taion being a bitch is just affect, not personality, but he’s really not even that rude or blunt, it’s more just that strong expressions of emotion don’t seem to come to him naturally so he has to be agitated into them.

Which is generally not a problem, when writing Taion POV, the way he performs his feelings for other people is quite clear cut, but when not writing Taion POV, people around him gotta prod deeper, to understand how he’s feeling. It’s not easy for anyone except maybe Eunie to gauge his emotional state, and the degree to which that bothers the others varies from Mio being largely used to it to Lanz who would find it constantly grating, not getting sufficient feedback on how they’re “doing”, basically. He’s kind of exhausting to deal with for people who are very emotionally oriented.

Also, I don’t think Eunie is the exception just for the soulmate reasons, but also because she’d cue pretty easily in on the “oh, if something is actually wrong, he’ll just tell me, it’s fine then” and focus on listening to his words, not his tone. I think a lot of their bickering is... if not performative, then at least the two of them agreeing, on some level, to die by the bit. It’s a lot more fun in mundane AUs where they don’t have magic soulmate mind-reading abilities and kinda just keep doing the thing in public because otherwise they would have to have the Conversation about whether they like each other or are just doing this in the absence of other options.