Energy Crystal

Energy Crystal, known as Energen Crystal (エネルゲン水晶) in Japan, E-Crystal (Eクリスタル) and EC for short, is an energy resource from the Mega Man series used for Reploids.

Mega Man X series
Energy Crystal is mentioned in some games from the series. In Mega Man X2, Crystal Snail took over an Energy Crystal mine. Tunnel Rhino from Mega Man X3 originally worked in an Energy Crystal mine before becoming a Maverick. In Mega Man X: Command Mission, the Gimialla Mine was an Energy mine.

Mega Man Zero series
In the Mega Man Zero series Energy Crystals appear as items that serve as currency and are also used to grow Cyber-elves. In Mega Man Zero 3, the Mod Cards 19 and 52 change the appearance of the E-Crystals. As there is an energy crisis during the series, Dr. Ciel created the Ciel System (System CIEL in Japan, Convergent Ignition by Energen Linkage) between Mega Man Zero 2 and 3 to solve the problem. The Resistance Base is also dependent upon E-Crystals, especially the teleporter in the commander's room as it uses plenty of power. In Mega Man Zero 3, a Giant Elevator was used to bring up a huge cache of Energy Crystals under Dr. Weil's orders. The exact reason Weil needed the energy is never revealed, although it most likely has something to do with Weil controlling the Reploids around the world via Omega and the Dark Elf. Energy Crystals are also implied to be the power source for Ragnarok's main weapon, a powerful plasma laser used in Mega Man Zero 4.

Mega Man ZX series
Like the Mega Man Zero series, Energy Crystals appear as items that serve as currency. In the first Mega Man ZX game E-Crystals are also used to repair damaged Biometals.

Other media
When Zero gets hungry in the Rockman Zero manga, Lito tries to give him human food, but Zero says he is unable to eat it and Lito wonders what a Reploid eats. Later, a Reploid from the Resistance gives an Energy Crystal for Zero.

Several years later, Omega needs many Energy Crystals to power the Giant Omega-DX, and steals several from Lito's house. The new Zero saw Omega and the two fight. Omega manages to escape, but without noticing his sack was damaged in the battle and he left a trail of Energy Crystals. Zero retrieves all Energy Crystals and finds Omega, fighting against him and his minions. When his minions are destroyed, Omega starts crying as he will be unable to build the Giant Omega-DX alone in three days and without Zero's Energy Crystals, saying Dr. Weil will fire him. Zero takes pity of him and gives the Energy Crystals to Omega, saying that he will help him in the construction.

Trivia

 * The Energy Tank was misnamed "energy crystal" in the North American Mega Man 2 instruction manual.