Do the characters come back often as well? I played a bit when it just came out but lost my account or something when my phone broke.
Yes, and you get these Blank Hero items more or less that will let you select 1 hero to claim (as well as Blank Memory Crystals to break their cap).
You usually get 1-2 of these per event, so you can pick some of your favorites if you're impatient waiting for them to come back around.
You do get some from doing Core Dungeons though, but the trade off is a Greater Growth Egg either way so up to you.