Sycorax

Sycorax is a death world of Ultima Segmentum, held by the Adeptus Astra Telepathica as a training ground where psychic storms force adepts to shield themselves or draw the weather down upon them. Imperial cartographers place it with low confidence and record a population of a few hundred thousand.

During the Indomitus Crusade Necrons assaulted Sycorax, taking much of the populace for experiment and sacrifice. Among the xenos host was a shard of the C’tan known as the Nightbringer, together with many Flayed Ones.

Uriel Ventris, newly crossed to Primaris, brought Fourth Company veterans including Pasanius Lysane and Learchus Abantes. Fighting beside Mechanicum forces from Lucius, the Imperial Guard and the Legio Astorum, they drove the Necrons from the world and defeated the Nightbringer shard.