Sky Lagoon

The Sky Lagoon was a floating colony from Mega Man X4. It was attacked by Mavericks and destroyed, and the Maverick Hunters pointed the blame on the Repliforce army. In reality, it was Magma Dragoon, a member of the 14th Unit, who after falling under Sigma's influence caused it to self-destruct and crash. This incident set into motion the chain of events known as the Repliforce War.

Other Media
The Sky Lagoon appears in the Rockman X (manga) where it is attacked like in the game. X, Zero, and the Maverick Hunters fight Eregion while Double watches in fear.