First brief profile for both characters:
Ghaleon was one of the original Four Heroes, was originally the Premier of the Magic Guild in Vane, and was widely known as the most powerful mage ever. He once competed with Dyne, his best friend, to see who would become the Dragonmaster, and narrowly lost. Once spirited and happy, he became melancholy with the death of Dragonmaster Dyne. he became mad at Althena because she supposedly sent Dyne to pacify the rampaging Black Dragon, which was laying waste to the land, leading to Dyne's "death" (actually, he just lost his powers and became Laike). At some point, Ghaleon found out that Dyne was alive. Ghaleon went insane over this as he felt that Althena and the 4 dragons shouldn't have needed to send his best friend out to die, and began to believe he should rule instead. After that incident, Ghaleon intended to capture and control Althena in a human incarnation.
Sephiroth was once the most powerful member of SOLDIER, Shinra's elite military division,who was celebrated as a heroic veteran of the Shinra Wutai war. After the war, however, Sephiroth was sent on a mission to the village of Nibelheim, wherein he discovered that he was the product of a biological experiment that combined a human fetus with tissue from the extraterrestrial lifeform Jenova. Learning that alien, his "mother," attempted to take control of the planet years ago, Sephiroth decides to follow in her footsteps. Sephiroth then burns down the entire village and kills many, but is assumed dead after a confrontation with Cloud Strife.A few years later, Sephiroth once again appears to continue his mission.
So yeah who do you think will win in 1 vs 1 combat also sorry about Ghaleon picture if it's too big kinda noob in these stuff. :P