Dark Power

Dark Power (闇の力) is an evil and powerful energy in the Mega Man Battle Network series that is created with negative emotions, such as hatred, and can't be destroyed as long as negative emotions exist. It is mainly used by Nebula and the Darkloids to increase their power, and spreads it with Dark Chips to taint NetNavis, creating Dark Souls that inhabit the Dark World.

Game History
In Mega Man Battle Network 4, Nebula spreads Dark Chips and MegaMan.EXE is infected with Dark Power when he uses one to defeat ShadeMan, leading to the creation of Dark MegaMan.

Later in Mega Man Battle Network 5, Dark Power is present in all Liberation Missions. Chaos Unison is the result of Dark Power. The Dark Chip Factory contains Dark Power in great amounts, and Nebula Gray is mainly made of Dark Power, which is used on Dark Chips. The Nebula Area (Murkland) also contains Dark Power, which gives power to the Chaos Lord.

Other appearances
Dark Power is also present in the MegaMan NT Warrior anime and the MegaMan NT Warrior manga.