Gemini (ジェミニ Jemini) is an EM being from the Planet FM, based on the Gemini constellation. He is Patrick Sprigs's compatible FM-ian, and when fused, they separate into two and become Gemini Spark (ジェミニ・スパーク Jemini Supāku). Gemini was the FM king's right hand man.
Gemini is quite disrespectful towards others and thinks highly of himself, and in the original Japanese language versions, uses rough language such as "ore", a boastful way of saying "I". He is also manipulative, but sometimes shows mercy in a way, shown in the games by killing Ophiuca for Mega Man on a whim and avoiding a fight with Mega Man when given the chance, and in the anime, offering Mega Man and Lyra Note the option to join him instead of fighting him. However, he is shown to be manipulative since he convinced Cancer Bubble to fill the Andromeda Key in the anime while he sat back, and in the games, convinced the FM king, Cepheus, to destroy the AM planet. Some of these traits seemed to have carried over to Pat as well in the anime. Gemini is shown to be extremely evil as well, since he didn't seem to have any particular reason for AM's destruction other than his amusement, and in the anime tries to use Andromeda to destroy the Earth just because he can.
Gemini is first mentioned by a Jammer to be an underling. He is then "shown" only by voice after Mega Man defeats Queen Ophiuca. However, instead of helping Ophiuca (a fellow FM-ian comrade), he decides to destroy her with his signature technique, Gemini Thunder. He later reappears in a computer space by himself, operating without his human "host". However, he states that his human host is "Rey," and leaves.
Gemini later shows himself after Pat decided to form a BrotherBand with Geo Stelar, but was interrupted by Rey taking over. He explained about Pat's identity disorder to Geo and Omega-Xis, then after Rey explained his history, Gemini merged with Pat and Rey to create Gemini Spark, with Pat being the Gemini Spark White and Rey the Gemini Spark Black. Gemini was destroyed when Mega Man defeated the pair.
He later returned after Cepheus, the FM king, resurrected him. Gemini, along with the other FM-ians, defeated Omega-Xis after he left Geo and retrieved the Andromeda Key. Afterwards, he found Geo at the underground WAZA station and tried to stop him from going into space, while revealing that he can transform into Gemini Spark through memory data alone. Gemini Spark was about to destroy the machine that could send Mega Man to space, but fortunately, Pat's intervention allowed Mega Man to fight back and defeat Gemini Spark, and destroyed the lightning duo, with their last words asking Andromeda to avenge their death.
Cepheus later revealed that Gemini was the one who tricked him into destroying the AM planet.
In the second game, Gemini Spark shows up after clearing the game in the Whazzap Ruins, where Pat finally decides to reveal to Geo about Rey being his evil other personality. Geo can then fight Gemini Spark in an attempt to help Pat suppress Rey. Like Luna Platz and Bud Bison, this most likely means that Pat still possessed enough residual energy of his FM-ian partner in his body to wave change.
In the Alternate Future, Gemini Spark IF retains the original's personality.
In the anime, the "Rey" personality is absent and Pat is a willing ally of Gemini. While Pat remains the white Gemini Spark, Gemini himself takes control of the black Gemini Spark. Instead of being loyal to Cepheus, they both plan to overthrow him.
Pat was originally a regular kid, until he got into a car accident. Gemini promised to save him in return for his help. He agreed, and the two became a fearsome duo that even Mega Man could not defeat at first, and needed Lyra Note to bail him out. His behavior was thought to be suspicious to his fellow FM-ians, and was one of the three extraterrestrial beings not "invited" by Cygnus.
Pat and Gemini both planned to take the Andromeda Key for themselves, but to do that, they needed to get rid of whoever had it at the moment, which was Cygnus (fused with Tom Dubius). However, the Andromeda Key broke while the rest of the FM-ians went on a rampage, and Geo and Omega-Xis (as Mega Man) stopped them with their newfound power, Cygnus being destroyed in the process. The electric duo repaired it, but its energy has been completely depleted.
Pat and Gemini created a duplicate of the Andromeda Key (which looked conspicuously fake from the audience's point of view), and gave it to Cancer Bubble and told him to fill it with negative energy, which instead would have filled their real Andromeda Key with the negative energy. However, this turned out to be useless since most of Cancer's (and the rest of the FM-ian's) efforts were either completely useless or was foiled by Mega Man. Gemini and Pat decided to harness the negative energy in a more effective way: to destroy the FM-ians and absorb their energy to the Andromeda Key. This, along with the order from the FM-ian king Cepheus to retreat, led Gemini and Pat to destroy their former comrades.
Gemini Spark Black first targeted Taurus and succeeded in destroying him and converting him to negative energy, then went to Wolf, Ophiuca, Libra, then Crown and Cancer with Pat/Gemini Spark White, although the latter escaped due to Crown's warning. The Gemini Sparks then targeted Lyra Note instead of Cancer (possibly because they thought Lyra was an easy prey at the moment or that Cancer was too weak to harness enough negative energies anyways), but Lyra and Sonia Strumm (Lyra's compatible human) were saved by the arrival of Mega Man. After Mega Man defeated the Gemini Spark twins, Pat had revealed himself to Geo that he was Gemini Spark. He left with an ominous message of Earth's destruction, revealing that even with the incomplete key, it was enough to activate Andromeda, which they did at once.
It's later revealed by Lyra after the battle that Gemini Spark had completely assimilated with Pat, destroying all of Pat's human consciousness. Omega-Xis states that the chances of Pat returning to his old self was around 0%, even if they did defeat the lightning duo.
Mega Man and Lyra Note went after Andromeda, which led them to Gemini Spark. They offered the duo to instead of fighting them, to join forces and take over the FM planet. Obviously, the heroes refused, which led Gemini Spark to attack the duo and sending them to the ocean floor. Fortunately, Cancer found the two heroes and woke up Mega Man, who went and found Andromeda and Gemini Spark in Japan. Gemini Spark ordered Andromeda to defeat Mega Man, knocking him out. However, the three Satellite Admins used their last power to perform a suicide attack to destroy most of Andromeda, and Mega Man finishes it off.
However, the fight was not over yet. Gemini Spark White killed Gemini Spark Black and harnessed his energy to power the Andromeda Key. Even though Gemini died, Pat still retained his Gemini White form and Gemini's personality. He reawakened Andromeda and repaired it, and released Andromeda's true power to destroy the Earth, and escaped to space, with Mega Man trying to catch him, and succeeded by grabbing him in a full nelson. To escape, Gemini Spark White threw the Andromeda Key down to Earth, which Mega Man went after to try to stop Andromeda.
Gemini Spark White declared it too late and fled. However, Gemini truly was destroyed when the FM King Cepheus returned Gemini Spark White back to Pat forcibly and erased his memories as Gemini, while dismantling Andromeda.
Gemini was previously destroyed, but he was revived along with most of the FM-ians attending Sonia's concert at the end of the last episode.