Yuu Gotou
In the present timespace, he is Haruka’s classmate and one of the protagonists of the anime. He, unlike other students, is being forced by his mother to go to cram school in order to pass a provincial enrollment test and go to a Tokyo junior high. As a result, he has little time for anything but studying. He initially tries to run away with disastrous results, and later has a blowup with his mother. Once the pressure is relieved, he realizes that he needs to take the exams because he has no special talents.
Yū initially doesn’t want anything to do with La’cryma and the Dragon Knights, because of Karasu’s contempt for him and Atori’s crazed behavior. But he reluctantly gets involved, eventually teaming up with Karasu to save all timespaces – and Haruka – from Noein. When confronted by the monstrous version of himself, he disowns Noein and destroys his power.
As the series ends, we learn that Yū is in Tokyo, having passed the exams. He comes home for vacation sometimes, and talks to Haruka constantly over email.
He appears to be physically weak and isolated, and he has the same angsty, doubting personality as Karasu – a fact that seems to irk the older version of himself. But he does have a very deep friendship with Haruka, and eventually realizes that he's in love with her. They even seem to have a psychic bond, since Yū hears Haruka thinking of him in another timespace.
There are other Yūs in other timespaces, some of whom lose their Haruka. Some of them remain as they are, but others changed radically because of Haruka. One of them, Karasu, becomes depressed and nihilistic, but is recognizable as Yū; Noein, on the other hand, is crazed and evil to the point that Yū disowns him.
