The Underneath

The Underneath was the home planet of the Shadow Kin. It was located beneath the rest of the universe. (TV: Brave-ish Heart) It had a blue star and was 9,000 years of space travel away from Earth. The Shadow King ruled from the Shadow Palace. (TV: Co-Owner of a Lonely Heart)

As long as they had an emotional anchor to latch onto, the Shadow Kin were able to create gateways from the Underneath to other planets, such as Earth, using their scimitars. (TV: Brave-ish Heart)

History
As Shadow King, Corakinus led an army in the War of the Underneath, (TV: Co-Owner of a Lonely Heart) beginning with an attempt at invading Coal Hill Academy. (TV: For Tonight We Might Die)

April MacLean and Ram Singh later visited the Underneath after April vowed to defeat Corakinus and get her heart back. She fought and defeated him, succeeding him as Shadow King. April later used the scimitars to create a portal back to Earth, and also used the portal to command her army to defeat an invasion of flower petals and getting them to close the portal once they had defeated the petals. (TV: Brave-ish Heart)

The planet was destroyed by Charlie Smith, using the Cabinet of Souls, after the Shadow Kin raged a war on Earth. (TV: The Lost)

Landscape
Some carved structures were present within the caves of the planet, as monuments to the darkness of the Underneath. (TV: Brave-ish Heart)

Culture
The idea of being intimate post-coitus was seen as baffling and almost disgusting. (TV: Co-Owner of a Lonely Heart)

According to April, the Shadow Kin's culture revolved around the belief that they were cast into the caves of the Underneath by the universe itself. As such, they prioritised the idea of destroying all life to ensure their own survival. (TV: Brave-ish Heart)