Looking for Literary technique's name

Narrative hook.

In medias res.

Non-linear storytelling.

Framing device.

This is an initial Flash-forward or prolepsis. The device may be used at any point in a tale (except at the end) and applies to your context.

A flash-forward (or prolepsis, also sometimes known as a flash-ahead) in a narrative occurs when the primary sequence of events in a story is interrupted by the interjection of a scene representing an event expected, projected, or imagined to occur at a later time. The flash-forward technique is used less frequently than its reverse, the flashback, or the flash-sideways.

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foreshadowing : an indication of what is to come

"If the history of the world were a novel, the events so strikingly chronicled in the photographs in this book … would seem a foreshadowing of the recent events …"

Merriam Webster