I think Tanabe-san is the author's self-insert.
Definitely. It's a pretty common thing to have a female side-character as a stand-in for the author in BL, and having said character help in resolving the MC's troubles adds to the author's feeling of "Yas! I am creating TRU LAV!"
....but I digress. I really liked Tanabe-san! While a lot of gay people hate being represented by the works of people of the opposite gender, because of their tendency to fetishize them, I just can't bring myself to dislike this story. Hayasaka-kun is clearly not transgender, yet he chooses to dress like a woman in everyday life because that sort of dynamic is important to his relationship with Yasuda-san. Usually, I would scream about how they're mixing up gay and trans identities, but here? It works just fine.
I just can't help but feel so goddamned happy for the main characters ;__;