plot twist : Kanda's sis is a dude

I think that's just how Kanda talks. For one thing, "Naru" is nigh-universally a girl's name in Japanese (even if it's a nickname, most names that start with "Naru" are also girl's names).

I suppose it's not impossible Naru is a crossdressing guy, but I'd peg it as very unlikely.

That explains why Naruto like doing the sexy jitsu so much

Nevermind, good call.