In my tskhn fic I had Hinata refer to himself AS Hinata instead of Shoyo and that was both a personal choice (I was and am more used to referring to him as Hinata, obviously) but it was also a thematic one of sorts. I think Hinata at the time of the show has (1) only rly just gotten on hormones, bc u have to be 15 to start hrt in japan + (2) probably hasn't been going by Shoyo for too long! It might still feel strange. I think hes v frenetic and nosedives into what he wants, but secretly feels more silly about himself and his desires than he wishes he did. If I ever get to my bipolar fic where hes on MSBY I think he'll be comfortably referring to himself as Shoyo. Prolly by mid 2nd yr / def 3rd yr it feels Very Him :+)
On the flip side! Throughout the entirety of this fic Kageyama refers to herself as Kageyama. Even when Hinata chooses to switch to her first name when they start properly dating (which they talk about + which kags tentatively agrees to; it's fine when its hinata, who asks, and fine when it's Oikawa, who does it bc shes Special To Him, whatever that means @ diff points in time; altho when her + hinata talk ab it, it's w the caveat that that might not always be her name!), she keeps referring to herself by Kageyama instead of Tobio. Which i like, personally. I think shes kageyama before anything else, even if Miwa is Miwa and Kazuyo-san is Kazuyo-san. It's not like she has a particularly strong rship 2 her parents, so Tobio rly only works as a distinction b/w her sister + her grandpa. Idk what I think her name will be one day, and idt itll come up in this fic by nature of her gender trajectory within the scope (where shes confused ab the rest of her career, she doesn't know what she wants more [or she's scared of what the answer is, more like] so "kageyama" becomes more of a mononym than anything else outside of Her Boys. Bc well. Distinctions, right?) Anywayyyy long winded but I dont think kags likes her name basically.