I want a yaoi or shounen ai in which the seme is biologically female, but identifies as male.

I AM NOT TALKING ABOUT SEME TRAPS OR GENDER-BENDER!

The seme has to be MASCULINE acting and looking, despite his biological sex.
One example is Yuureitou, a manga with a FTM seme.
Once again, I am not talking about manga like Otoshiana ni Hamerarete, in which the seme is biologically MALE(not to mention girly looking).

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Unfortunately FtM representations in manga are quite rare even more transmen in a BL setting. If you do an advance search with the tags "female to male" and "transgender protagonist" or "transgender character/s" that will give you an idea, furthermore quite a few of the results are not yet translated and a few others use a body swap kind of setting more for comedic effects.
You might have more luck finding something like that in western webcomics, "With Great Abandon" on tapas is one of my personal favorite for example ( https://tapas.io/episode/550592 ).