In Medias Res

A narrative work beginning in medias res opens in the midst of action. Often, exposition is bypassed and filled in gradually, either through dialogue, flashbacks or description of past events.

Works that employ "in medias res" often, though not always, will subsequently use flashback and non-linear narrative for exposition of earlier events in order to fill in the backstory.

For example, eden* opens with Ryou and Sion already living together in the mountains and later fills-in the backstory with a lengthy flashback.