Kokuro

After receiving a message from Rin ASHIBA, the girl he's in love with, Sora ISOSHI goes to a classroom at his high school where Rin had asked him to meet. But when he gets to the classroom, he finds himself alone. Thinking it was a joke, he leaves the room, but once outside, in what should be the corridor of his high school, he sees instead a large white room where, sitting on a throne at the back of the room, is Rin ASHIBA.

She tells him that he has been chosen by the Tower to try and climb it and become its new king.

But as he wasn't born into this world, he doesn't have the ability to use what all the inhabitants of the planet are able to use, the Ushi.

So Sora is given a strange power. A power with which he will try to climb the Tower, trying to fulfil Rin's wish and thus become the new King of the Tower.

Heat, Ushi and Catalyst