Arago

also known as AR∀GO or AR∀GO: London Shikei Tokushu Hanzai Sousakan is a Japanese manga series written and illustrated by Takahiro Arai. It was serialized in Shounen Sunday. AR∀GO was published in Italian by J-POP from September 22, 2009 to July 20, 2013.

Plot
The story centers around twin brothers, Arago and Ewan, whose parents were slaughtered by monsters. Years later, the vengeful Arago crosses paths with Ewan, who has since become a police officer, just as blood begins to flow again in the streets of London.