After conquering a certain amount of Timeline Stability in a Timeline, you will have the chance to encounter a Quest Echo, which represents a pivotal moment in the story of a Timeline.

The final Quest Echo in a Timeline is a boss fight, and by defeating it the adjacent Timelines will become unlocked.

Quest Echoes appear in the same order each time, and all Quest Echoes for the current Timeline need to be completed to unlock the next Timeline. In Empowered Timelines, Quest Echoes are optional and are not required for challenging the boss of the Timeline.

Dying in a Quest Echo will reduce your Timeline Stability, but cannot undo your progression through the Quest Echoes.