Albedo Piazzolla

Like his conjoined twin Rubedo, Albedo Piazzolla is a U.R.T.V., created by Dmitri Yuriev to combat U-DO, a mysterious wavefront existence. However, unlike Rubedo, who was able to stop his ageing, and Nigredo, who was still able to age and be injured, Albedo became immortal, and the thought of going through life without both of his brothers unhinged him mentally, and he disappeared after he was saved by Sakura Mizrahi during the girl's Encephalon jump, which killed the girl. Even though he hated her, Albedo felt guilty over Sakura's sacrifice, which would lead him to his obsession with the Kirschwassers and MOMO, which were modeled after Sakura.

As was said before, Albedo is immortal. He had, after he kidnapped MOMO to access the Y-Data within her database, shot himself in the head with a laser blaster in front of MOMO—and the head grew back! He is also obsessed with reuniting himself with Rubedo, which Albedo irrationally believes hasn't gotten over losing him to his madness.

(Source: Absolute Anime)