1. Idyllic Past Protagonists in Noir tend to have mostly happy backstories... or at least backstories these characters romanticise and look back on with rose-tinted glasses. Characters in Noir spend a lot of their quiet time reliving these happy moments, because...

2. Moment of Rupture ... these happy moments end tragically and violently before the start of the story. Something happens, whether external to the characters or through the characters' own actions, that causes the idyllic past to end.