Gaah, I completely agree with you! I'm Nana bias too. I hate how she weren't view as a person at all, but just a mere subconscious of yaya even though she have just as much power as yaya. It would have been nice if Nana have her own love story but I guess that would create a whole other drama about love triangle. Moreover, If you think about Nana x Moriyama, Nana would have love Moriyama just as much as yaya but to know that he don't even love her that way and he only want to confess to yaya is kinda sad.
Tbh I kinda shipped Nana X Shohei and Moriyama X Yaya...
Somehow Yaya just really pisses me off. Naiveté and spinlessness must have a limit, right?!!! Apparently not; she just takes whatever anyone throws at her and then hates herself afterwards. Tbh, I wouldn't have minded all that much if Nana just took over forever but I know that wasn't the point of the manga. It's about self-acceptance and the changes that can come from it and blah blah blah. It's just a little hard to like someone who only knows how to be a doormat.
Gotta wonder what Moriyama saw in her, especially considering what his ex was like (maybe he was looking for a girl exactly opposite her?)