There's a girl from Diary of Our Days at the Breakwater, Makoto, who I have always headcanoned as being Glasses-kun from Non Non Biyori, post-transition. This started out as just a little joke between me and my mom about how these two characters looked kind of like gender-swapped versions of each other, but I kind of took a liking to the idea of them actually being the same person — at the very least because trans characters pog, and connecting two similar fictional works I like to each other is also pog. Keep in mind that I haven't finished the NNB manga, never read the Breakwater manga, but have finished either anime (though I might not remember every detail from either).

As unlikely as my little "Makoto is Glasses-kun" headcanon is, it's still fun. It's still an exercise in imagination, to imagine how Non Non Biyori's character who never spoke or smiled or really had any presence at all might've had some issues she was secretly working through in the background; and how the growing independence of high school life, where she was commuting to the city by herself and making friends outside her small town, might've facilitated her questioning and experimenting. How after her coming out to mother Yukiko went poorly, that she might've actually been disowned, and had to move in with some more progressive relatives, whose surname she took on for a "clean break" from the old life.

I guess another way to put it is that the most unlikely trans headcanons are also the most fun fanfiction prompts!