It seems like they has been many appearance with Rangiku and her female Soul Reaper crew for the past few events. This time, the female Soul Reapers will be doing a fundraising event!
During this event, defeated enemies may drop rare characters while bosses may drop 4* Soi Fon. There is no limit to the number of 4* characters you can earn in this way.
Chance for the below characters to drop during the quest.
3* Rangiku, 3* Momo and 4* Soifon
For more information on the event, check out the guide here!