@JavelinJoe hmmm. I might be able to shed a little light here. I'm trans myself, and Hina does not fit the standard of a boy with GID (gender identity disorder). If anything, I feel more like Hina is somehow a... 'reverse-trans'. Not that that makes much sense, since that'd make him a cis? Or, possibly, he's more similar to a post-treatment intersex at this point I guess. Basically I get the impression that Hina is deadcenter on the gender spectrum, and is currently so outwardly female because of their environment influencing them so heavily.
Typically, a kid with GID will live with great emotional and physical pain brought on by their sex not matching their gender, often venting their frustration with either self harm, apathy, or 'over compensating' (such as a male with a female gender doing body building to convince themself that there's no problem when infact there is). Hina exhibits the opposite of this, so Hina never really seemed to have GID in the first place. Instead, the initial Hina is "so genderfluid it hurts" or something nonsensical like that. I dunno, I'm not a trap.
Aki on the other hand, DOES exhibit symtoms of GID, as does Yuuri and Myaakowhatshername. Goriyama was just so happy not to be ugly anymore and took whatever he could get.
Honestly, if I'm right, I kind of predict Hina to end up as a futanari at this point lol.