I'm beginning to think Keisuke was a maiden at heart from the start. Not just expressing envy towards girls in the first chapter, but to the point that lifechanging wish slipped out. It's 100% something you see gender nonconforming guys and trans girls do a lot. "This girly stuff makes me happy, I need to share it with my other guy friends so they don't feel left out! We can be girls together!"
I think it's funny Kaneko Naoya got brought up in the credits because they're a great example of that. TS School pretty much runs on that wholesome but ultimately somewhat misguided energy.