I think MarriageToxin fans are failing to consider that Kinosaki is both genders. They're both. She literally says she's both. He's comfortable as both. "Block me if you think Kinosaki's a man/woman-" My siblings in queer, can we not die on a hill that's already been conquered? They're both.
And that's not even getting into the fact that you can't try to slap USAmerican queer culture on a Japanese queer character. Japanese gender identity is its own thing. They've got their own culture going on there. There are certainly points of intersection, but a Japanese person isn't going to express their gender in the same way as a USAmerican, trans or otherwise.
And this isn't me saying you can't headcanon as you want, and I understand the desire to see yourself reflected specifically in a genre where you don't often see it, but please just be sure to acknowledge the things above, and don't harass someone for utilizing the canonical text as it is presented.
