this..... feels like a strange BL ending....
Yes- No- Umm..... bisexual for each other....? Tetsuo is still a transman and Taichi is a dude crossdressing
Yeah, a good ending with some vagueness left there in terms of what they are for each other at the end? I THINK it's Taichi embracing either genderfluid or closeted trans, maybe? Or perhaps only crossdressing, and Tetsuo accepts that being bi/gay doesn't mean not being a man? Or possibly just that Taichi is special enough to him that it still works, even if he's still mostly straight? Unsure, and probably intentionally so, but whatever it is fits in with the "humans are complicated but society has a big problem when people don't fit neatly into categories" theme.
And also the theme that money and power are the key to surviving when you're unusual - if you're weird AND powerless, society will grind you into the gutter