Will Tetsu feel the same way after Mogumo grows up and goes through puberty? He's never shown attraction to any adults, so it's hard to judge his preferences. Would he feel the same way about Mogumo if he didn't work in a girly boy cafe with his brother?
Statistics tell a harsh story. Ben Shapiro memes have fallen out of favor, but some are still relevant. Especially the 2% = 40% which should be the most alarming.
The worst part of Mogumo's situation, is Tetsu is basically taking advantage of him.
Tetsu doesn't identify as a girl, he's stated that multiple times. He likes the trends and fashion of women. But these things are only considered feminine by society. Mogumo was desperate for acceptance, and he met Tetsu, who encouraged his interests. If Mogumo met a girl that also encouraged those interests, there would also be affection.
Tetsu is basically using Mogumo's dependency as a way to get physical gratification. And part of that was bringing Mogumo into a place he controls, the cafe. The boys in the cafe weren't really the same as Mogumo, but in a way Tetsu guided Mogumo into becoming like them and his sibling, who actually does identify as a girl. Tetsu groomed Mogumo into being the partner he wanted, although I think Tetsu thought he was just helping.
It mirrors Suzu and Haruto's situation in the author's hentai story in the same universe. Where Suzu is taking advantage of Haruto's fetish to rope him into a relationship.