The Story of Nocturne
Nocturne is not a creature with a history, exactly. It is a phenomenon given a body — the aggregate nightmare, the thing that has no name but lives in the space between sleeping and waking where conscious defenses are down. Every sentient mind produces fear in the dark, and Nocturne is the entity that was assembled from those fears, or that always existed to receive them. The metaphysics are ambiguous. The result is not.
It escaped into the waking world through a summoner's miscalculation during the era of the League of Legends — a mistake that released something that had never been meant to have physical form, a nightmare made manifest and suddenly capable of causing the suffering it had previously only reflected. The terror Nocturne produces is not strategic or purposeful. It is instinctive, reflexive, the act of a thing that exists to generate fear expressing its nature as directly as possible.
It kills because it wants to. It spreads darkness because darkness is its medium. It is not plotting anything; plotting requires a goal beyond the immediate expression of its nature, and Nocturne doesn't have goals in that sense. It is threat at its most elemental: violence without agenda, darkness without purpose, the nightmare that exists simply because minds exist to have nightmares. If it has a preference, it is for the moment just before the victim understands what's happening.