I'm not sure how much you're looking for castmates, but there's a Sheryl at acatalepsy_rpg, and I've definitely been thinking about sending Mikumo or Klan there next round in addition to my current character! It's a fantasy world-hopping game where characters are pulled into a sort of hub world by a witch named Astoria and then sent out to other worlds to save them from various dangers. Characters also get a single power on coming in (while losing their canon ones) that can be just about anything that isn't game-breaking, so that's a fun bonus. I'd say it's around medium pace and it definitely seems to be backtag-friendly from what I've seen so far, so it checks those boxes too.

Unfortunately apps don't open until near the end of next month, but I thought I'd suggest it since I was happy to see a Ranka around!

Admittedly I've only recently joined, but from the impression I've gotten of the pace, there's some people who are faster and can boomerang, but others prefer to tag every two or every few days, so there's a range that I'd say averages to medium from what I've experienced so far. And ty, I only got into the franchise relatively recently but I've been greatly enjoying both the characters I picked up from it! Also it's nice being able to find occasional castmates since I usually pick bad canons for that...

But anyway, good luck in your game search!