Update from Serina (thx again SuzukiRyo) :
I dunno why, Serina is less popular in Nikkisei, is it because she's a quiet type-girl??? (compare with Umeko, Amimi, Nao). Didn't you guys see in Idoling!!! episodes that Serina sometimes get "cold" responses from the other member?? I saw sometimes she's being ignored too.
I think she have started her career in Idoling!!! with great experience record, such as Oha Star girl. As i know, she was also child actress (like Ashida Mana). Also her love of anime should be advantages to become more popular (member).
IMO she's cute, combine with Chubby looks
She's still young (youngest in Nikkisei), also have a lot of potential. That's why she's one of my fav. members (beside Kaorun, Ruri & Maipuru)