Noein

He is the eponymous antagonist of the anime, initially appearing as a floating mask over a spectral body, occasionally revealing himself to "rescue" Haruka and eliminate any who interferes. But in reality, Noein is another Yū from a different timespace where he survived the car crash that killed Ms. Yukie, Isami, and Ai while forced to watch a dying Haruka be consumed in the ensuring explosion. Unable to bear the pain of losing Haruka, Noein decided to look for a new Haruka in a different timespace only to find that every Yu in within other timespaces suffers the similar pain of losing his respective Haruka, and that each timespace was filled with pain, death and sorrow.

As a result of his eyes opened to the truth, Noein decided to converge every timespace to stop all the pain and sorrow, creating Shangri'la as the first step of his plan: To use the Dragon Torque's power to erase all existence and start things anew. In the process of this intent, Noein loses his own humanity to the point of resembling an emaciated albino version of Karasu upon removing his mask and emerging from his gelatinous covering. Though he is still clearly in love with Haruka, Noein's feelings warped into a twisted love/hate for not only her but his other ignorant selves.

As a result, though he was Yu once, Noein is no longer the same as his other selves as he lacked the ability to truly remember his past. He is even more nihilistic than his La'cryma counterpart. In the end, Noein's existence was denied by Haruka and his other selves. Unable to cope with this as the dimensions recreated themselves, Noein lamented "Who am I?" as his minions emerged from his body and hovered over his dying form, with only his mask and vow that his vision will be realized remaining. [Wikipedia]