I'm not even going to bother arguing about the confession for now. I'm going to let the Mikubros have their day in the sun, even if this is about as weak a confession as we could get
But I'll say thi, Miki is most definitely not in the lead. She's not really even.in
the running because she hasn't been special to him and he doesn't have even an embryonic romantic interest in her. He hasn't figured out everything, but we the readers have been shown enough to make that judgment. At the very best she's tied with Nino. There's no way what happened here trumps Nino's, even though she said something about wanting to learn about each other. Nino's been doing that for ages because Fuu has been so damn persistent with her. Now it's his turn to learn about her.
Enjoy your day. It won't last.