I'm gonna be thinking about this all day
If you deadname someone in the death note it kills you
In one of the Death Note live action movies (I think it was Light Up the New World), a man changes his name after harboring guilt about past crimes and trying to atone (not even answering to that name). He's only killed after his new name gets put in the book, since he shed his old name.
Man wasn't trans, but if the logic applied to him, logic should apply to trans people too!
This rule implies that birth names are not necessarily the names given to you at birth.
That means you can change your name or consider yourself to have a new name and the death note recognizes it.
Death Note is an ally.
Okay, hear me out.
Batman Beyond establishes that Batman considers Bruce Wayne to be the mask and he thinks of himself as Batman, meaning that in order to kill him you'd have to write “Batman” into the Death Note.
However you *also* need to picture his face. So you'd need to know that Batman is Bruce Wayne, AND that Batman ISN'T an alias but his true name.
Batman is... INCREDIBLY difficult to kill with a Death Note.
Also, like L, he is considered to be the world's greatest detective...