Mineral Zone

The human survey and mining ship Tessera reaches Vesper, a planet orbiting the orange star Khepri, to investigate the Anomaly: a gravity disturbance above a region full of impossible crystals that the crew calls the Mineral Zone.

When the pilot cuts into a giant violet crystal there, it shatters and tears open the Seam, a place where our universe nearly touches a dying neighbouring one, and the ship is pulled through into another version of Vesper with no contact to the crew.

Every night the Choir pours out of the rift: shifting, multidimensional beings escaping their collapsing universe, who can only be destroyed by sunlight and lasers tuned to it.

VAEL, the last guardian of the vanished Aurith, has no body and cannot fight, so it guides the pilot through building a base, holding off the Choir and turning its shards into new technology.

The portal VAEL opens doesn't lead home, though; it drops the pilot back at the start of the mission in yet another version of Vesper, trapping them in a loop until the Anomaly is closed, and there are infinitely many Anomalies