His "I'll fall in love with someone different...but that's TOO different, so NO WAY" and the her "He's into guys, I'll cover that with pants and a wig!" is absolutely bound to meet in an unfavorable place (bloodshed, blunt trauma, mayhem)
I mean, she's basically just what he's looking for (different, alright, check).
Nao probably thinks that Saiga will be like, "I like guys but you're special because you're the only girl I'm attracted to."
Homophobia but with little steps
Ok but let's just follow her logic and say that he was really into guys, does she think that if he'd fall in love with her while she's dressed as a dude, he'd automatically still want to be with her when he inevitably finds out that she doesn't have a penis after all? Like, now he's magically not gay anymore?? Or does she intend to drag this on forever or maybe even have a sex change?? Her reasoning is so wild that I have to read this just to see where things will go