Most definitely Momiji. There is more people subbing that character than maining that character (in the past it was Hitomi). Could also add Honoka and Rachel in that department of pocketed characters.
I used to think momiji was everyone's favorite side chick, alongside with rachel, but I can't recall the last time I've even seen a momiji sub, hell of a lot of Mila subs out there though, id even say honoka is getting up getting there in popular side chick status
Ugh, I remember when half baked hitomis were everywhere, so annoying, also there was a time when rig was a popular pocket character? that must of around the time I stopped playing cause I dont remember that being a thing at all