War of the Underneath

The War of the Underneath was a war involving the Shadow Kin. Corakinus led them in battle. (TV: Co-Owner of a Lonely Heart) The war had stemmed from the belief of the Shadow Kin that they were an evolutionary mistake that the universe had abandoned. They had come to the conclusion that it was necessary to fight for their existence since the universe did not care. (TV: Brave-ish Heart)

One part of the war was an attempt at invading Coal Hill Academy in October 2016, which was foiled by the Twelfth Doctor, a group of students and a teacher. However, a few students were killed during this attempt including Rachel Chapman. Corakinus' advance scouting of Coal Hill before the invasion attempt also led to him sharing a heart with April MacLean, after he was partly hit with a blast from a displacement gun. (TV: For Tonight We Might Die)