Here is the full list of all 9 Timewell: Trail of Celestes achievements.
Survive the encounter with Cerberus in Urur
Survive the encounter with Leviathan in Tempest
Survive the encounter with Twins in Tempest
Finish all story chapters
Destroy 200 Daggers
Destroy 200 Turrets
Destroy 100 Cloaks
Destroy 100 Hunters
Destroy 200 Kamikazes by ramming into them