Archer

In Fate/stay night UBW:
He is the Servant of one of the series' main heroines, Rin Tousaka. Due to an incomplete summon, he apparently has no memory of his previous life or identity. Archer is sarcastic and cynical but under his hardened exterior lies a complex and dark personality that unfolds throughout the story. Though skilled with ranged weapons, he can hold his own in melee combat. Archer considers Shirou Emiya's idealism to be weak and delusional, recognizing the mentality of "wanting to save everyone" as naive and impossible.

Archer is actually a future version of Emiya Shirou, who became a hero through Emiya's wish to save innocent lives. After his death he became a Counter Guardian, a Spirit deployed to maintain balance and prevent humanity's extinction, but without the ability to act on his own he was forced to kill and face the fact that his ideals were not realizable time and time again.

To escape this cycle the only hope for EMIYA was to be summoned as a Heroic Spirit and kill his past self before he became a Counter Guardian, which would cause a time paradox and release him from the cycle.

In Fate/Grand Order - First Order:
EMIYA was Blackened, a process by which a being is tainted by an outside force, causing their personality to be reversed toward the orientation of evil