Why all the hate for Ragnarok Odyssey? It's a little overpriced at the moment, but it is easily the Vita game I've dumped the most time into. If you have Vita friends IRL, it's the best local co-op game on the system, and a decent short-burst grinder.
Sure, Soul Sacrifice may render it redundant, but still. It's a lot of fun.
It's not MonHun.