Dark Power (闇の力 Yami no Chikara) is an evil and powerful energy in the Mega Man Battle Network series that is created by 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 is used to create Dark Chips to taint NetNavis with Dark Souls.
In Mega Man Battle Network 4, Nebula uses the Dark Power to create and spread Dark Chips. MegaMan 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. It is revealed near the end of the game that Dark Power is harnessed through the use of the SoulNet, after which the Dark Chip Factory is used to graft it onto chip data. Nebula Gray is mainly made of Dark Power, and Nebula Area (Murkland) also contains Dark Power, which gives power to the Chaos Lord.