Kastuvis is a Death World in the Astoth sub-system. Whilst technically under the governance and protection of the Tempest Angels, there is not much to govern and so are largely left to their own devices. The population is estimated to be in the low thousands, clustered in a few settlements that rely on each other in the constant battle to survive every day. Kastuvis is divided into two types of terrain; the first of which is the mass of purple-hued jungle that is home to a variety of predatory beasts and poisonous plants, all of which seem determined to kill anything that isn't them. The other half of the planet is a sub-zero ice tundras that carry on as far as the eye can see, utterly deserted aside from the local polar beasts that do not take kindly to strangers.
This planet is used by the Tempest Angels for their exposure trials for aspirants of the Chapter. In the past, it has been known for them to stray from their usual selection pool of Astoth to select a handful of noteworthy aspirants from the local populace, renowned for their fortitude and gritty determination. It is also used for further training after the trials to further hone the skills of the Astartes.