Andromeda - S1.E54

Revived, Andromeda proceeds toward Echo Ridge, annihilating cities in its path. Mega Man and Lyra Note attempt to stop it but are overpowered. Lyra Note is left incapacitated, so Mega Man proceeds alone with Star Force, but his attempts are in vain. Amidst the battle, Luna, Bud, and Zack witness Mega Man revert into Geo (Luna was only half-conscious at the time, and this shows in later episodes, where she says that it's impossible that Geo was Mega Man).