MegaMan Star Force 2: Zerker X Ninja

AM
AM-ians are characters from the MegaMan Star Force series. They're EM wave beings like the FM-ians and live on the planet AM which is neighbors with planet FM. Cepheus, manipulated by Gemini, used Andromeda to destroy planet AM and many AM-ians. However the 3 satellite Admins, Leo Kingdom, Pegeasus Magic and Dragon Sky survived. Omega-Xis was an AM-ian but was on Planet FM at the time of the attack. The attack on planet AM prompted him to steal the Andromeda Key and plot to use it to get revenge on Cepheus. In MegaMan Star Force, after defeating Andromeda the Satellite Admins will appear and tell you that some AM-ians have survived and are living on other planets. Then they and Cepheus leave to rebuild Planet AM.

MegaMan Star Force
The FM-ians mention it during their raids on Earth, and apparently, Omega-Xis has something they need to activate it- the Andromeda Key. Ophiuca states that it needs two things: the Key and the FM King's control panel. When Omega-Xis leaves Geo, the revived FM-ians ambush him and, despite Harp Note's attempt to help, succeed in taking the Andromeda Key. Apparently, they plan to have Andromeda consume all life and destroy planet Earth, just like it destroyed Planet AM. They start kidnapping people to feed them to Andromeda, but are thwarted by MegaMan and the Satellite Admins.

Later on in the Space Station Peace, after MegaMan deletes all the FM-ian warriors and confronts the FM King, Cepheus, the FM King summons Andromeda. Omega-Xis states that it has an EM body, but all it ever does is eat other EM beings. Half-way through the battle, it transforms into a it's robotic form. After MegaMan defeats Andromeda, Cepheus sends it for another go at MegaMan, and Geo can't fight anymore because of the King's strong Z-waves. However, it goes cannibalistic and tries to eat Cepheus, but Geo is still helpless. Geo then remembers his friends who are depending on him, and his father, and that gives him strength again. Using one powerfully charged shot, he destroys Andromeda once and for all, saving Cepheus and planet Earth. Geo and Omega-Xis both forgive Cepheus.

Andromeda can be fought in the last wavehole in the Space Station, beyond Ophiuca's door. Once you pulse in, you can't pulse back out until you defeat Andromeda. It can fought repeatedly so long as you still don't have the 6 icons. After defeating it, then defeating the version's Satellite Admin, he tells you to fight the "truly lonely giant". After getting all the icons, going to the place where you find Andromeda will let you battle Andromeda∞ (4000HP). It then stays permanently in that form, and can't be reversed back to its original form. Beating this means you've finished the entire game and it's secrets, with an extra screen at the end showing Geo and all his friends and commending the player for his efforts.