Have you considered tushanshu? We hit all of your preferences except castmates--we're smallish/mediumish, no memory or power loss, and we're super backtag friendly! The genre of the game is kind of a fun mix of adventure/politics/slice of life, and it's easy to lean more toward whichever amuses you the most. The metaplot is huge and there are tons of awesome NPCs, although I tend to lean more toward the slice-of-life/personal plot end of the spectrum.

Apps and reserves are always open, and there's a TDM up if you're interested!