Fused Colony

Fused Colony (黒けぶり, Kuro Keburi, lit. Black Smoke) is a mysterious humanoid shadow creature that's formed from a large amount of Kabane that have combined/fused together.

It chooses a Kabane to become it heart. If said Kabane got eliminated then it would be defeated, otherwise it would just keep reforming. As stated by Mumei, the fused colony is very greedy, taking in humans and Kabane to grow.