Energy Element

Energy Element (エネルギー元素), also called Energy Crystal (エネルギー結晶), is a type of energy resource from Mega Man 3 needed by Dr. Light and Dr. Wily to be used on the giant peace-keeping robot Gamma. Mega Man must obtain eight Energy Elements protected by the game's Robot Masters. After fighting against Break Man, Dr. Wily steals Gamma, also taking the elements. The Energy Elements were never shown in the game, and it's unknown what happened to them after Gamma's destruction, presumably being lost or destroyed.

Captain N: The Game Master
In episode 32 from the animated series Captain N: The Game Master, the Energy Elements are called Energy Tanks and resemble a large, yellow Energy Tank with a blue dome above. Mega Man obtains the last Energy Tank after defeating Top Man, and it is placed inside Gamma.

Mega Man Gigamix
The Energy Elements appear in the manga Mega Man Gigamix, and have an important role in the stories. In volume 1, they appear in the story Asteroid Blues, which is based on the events from Mega Man 3. In volumes 2 and 3 they are shown to have a connection with Duo and the Stardroids.

Mega Man (Archie Comics)
Although the Energy Elements have yet to make a direct appearance in the series, their presence was briefly implied in Mega Man Issue 20, when Mega Man briefly fought against Gamma when stuck in a time loop.

They also received two other mentions, both in the crossover arc Worlds Collide (specifically, Mega Man Issue 24 and Sonic the Hedgehog Issue 249), and both relating to the Chaos Emeralds. In the former, Dr. Wily briefly pondered whether the emerald Flash Man had detected was a new form of Energy Element after Ra Moon detected it as having a huge power output, and in the latter, Sonic the Hedgehog commented that it would take over a billion Energy Elements (when Mega Man explained that they were his world's most powerful energy source) to equate to the power output of one Chaos Emerald.