Manga with trans masc characters! Including main and supporting, I have not read all of these but I will put little notes on the ones I have read :3 Manga not included because it's not on the site: Chiguhagu (translated)...
These manga feature LGBT themes that focus on gender and gender identity, including trans-related topics, rather than the sexuality side of the tag.
A comprehensive list of manga that feature transgender characters and themes. I'm still evaluating some other manga, but if there are any I've left out, or if you find an error, PLEASE let me know in the comments. ...