Do the gemcha/ gem quest cycle if you haven't already.
You'll even get a small elixir bonus everyday once your energy cap becomes high enough (started being very noticeable around 95 energy cap ish)
Double post edit: In the DMM version, apparently Summer Sol, Brynhildr and Nergal are available again.
Guess this means limited edition hime aren't really as limited edition as much as "appears once a year for one month" kind of deal?