The best place for character fodder drops was the anniversary event. I'm not sure if you farmed it or not, but I ran the hell out of it (both single-player and co-op when my tickets ran out). I fully ascended a lot of my 5* and three of my 6* (Soi Fon, Kenpachi, and Shinji). It was amazing, and so many accessory drops too (and hearts to level them!). Sadly, it's gone now.
The Omaeda event is okay, from I've seen so far. Yoruichi drops pretty decently, but aside from that, it's going to be slim-pickings. Hopefully we get another lottery event soon with nice drop-rates. Supposedly, we're getting a summer-themed event (with that 5* summer Toshiro as the top reward) soon, as the code has already been data-mined in the game. So maybe that will be better? It should start sometime this month, while the summer gatcha is running. Maybe after the current event ends.
I'd actually like that 4* Rukia though, haha.
Oh! You already know this if you've logged in, but 15 million download event is now going on! Plenty of free crystals (and jewels, for leveling your new 6*), gold (which you'll need, for the aforementioned 6*), 75 Spirit Orbs over the course of the event, and a few more things. Not bad.
BTW, I tried the swimsuit characters (from the Free Play) in the gatcha, and I'm definitely skipping. The only one that seemed reasonably fun was Yoruichi, but the rest seemed so...bleh. Their stats might be nice, and they might get a few 6* abilities that'll help with their damage, but their actual move-sets are so boring. You can tell they were developed early on, when the game was still young. We've come a long way since.
