All character backstories in A Hat of Time. You can unlock these pictures by collecting every photo in the Purple Time Rift stages.

Mafia Town unlocks the backstory of the Mafias as well as the chef.
Battle of the Birds unlocks the backstories of DJ Grooves and the Conductor.
Subcon Forest unlocks the backstories of Queen Vanessa and the Snatcher. (This is by far the most interesting one)
Alpine Skyline unlocks the backstory of the goats, or whatever they are.

A Hat in Time playlist:    • A Hat in Time