I have skimmed through a few posts and am a little disgusted in people debating whether or not Kokoro is a good or bad character. She is pretty damn terrible. I mean she got hit in DOA5 in 1.03a, but myself and the other top Kokoro players still stuck it out with her, but in 5U she got hit even more to the point where she is too inconsistent of a character.
She is so bad that Artemis and myself have taken on new mains/secondaries just to get by, and E-mann just dropped her completely. She seriously needs some help in this game.
From what I've seen of the Japanese tier lists, they have always believed her to be a top tier character. I'll leave it to you to take that information into thought as to why she hasn't received any buffs...