I play it for Sanya. Only Sanya, always Sanya.
And the game's a lot less dull if you build an auto clicker that plays it for you. The actual battles themselves are rather dull, but the vast amounts of ways to set your characters up prior to battle is rather interesting to dabble with.
I have Sanya and Lynette as my main attackers because Sanya is Sanya and Lynette gets a free +100% attack boost, with Eila and Miyafuji throwing out support cards. The current event's card is for Eila, but gives Sanya a 150% attack boost and +5 to number of hits, so it's pretty awesome for my setup.
But of course, the fact that I can touch the game maybe the first 3 days, leave my auto clicker on whenever I'm at work/sleeping and still remain in the top30 shows how dead this game really is. Still, it's the only way to get new Sanya on a regular basis.