Thanks, Grace. I'm not finished yet, though. Some of their stories really come into play when selected as the unit's leader in Story Mode.
i.e. Sakura has a bad history with one of NAZO's members. She feels like she has to perform at her level in order to catch up with her and thus changes her styles of practice and performance entirely. Because of this, she begins to lose her appeal. Sakura almost quits her job, feeling like the gap between her and her rival is just too great, but with a little help from Kenji and Haruka, she regains inspiration and remembers why she wanted to be an idol in the first place...it's fun for her and loves bringing smiles to all who listen to her voice.
Asuka's weak constitution comes into play and challenges her career. NAZO's spiteful producer tries to take advantage of it.
Nozomi is at a different level than her partners. With the looming threat of NAZO, she starts to push them beyond their limits, believing them to be holding her back. However, everything changes when NAZO's leader tells her that she's the unit's weakest link. While this does shock her at first, she eventually accepts this and changes her style so that each member flows together perfectly.
Sorry if I spoiled anything, but I thought I'd give some examples. Stay tuned for more brief bios.