Yokai, if bothered, can be dangerous. They don't do it because of evil intend however. But there are some Yokai who would rather harm than do good.

Plot #1:(Human) There was a huge cloud that corrupt Yokai all around except for a good few, which is good, however that means the human world is no longer a safe place and the yokai begin to terrorized the place. Once you entered the Yokai World..it's even worse than you thought

Plot #2:(Yokai) You are one lucky Yokai, not only did you survive a attack, you survived a huge curse. But that doesn't mean you are safe, you and every Yokai that weren't corrupted are now in danger and so are the humans. You have found ways to save the humans, but it's never enough. You have to find the source of it all