Seifer Almasy (サイファー・アルマシー, Saifā Arumashī) is a classmate and rival of Squall, who can only be controlled by the player during the Dollet sequence. He reappears as a boss later in the game. He acts as a foil to Squall in many respects, having dated Rinoa before she met Squall, and assuming a leadership position among his friends. Like Squall, Seifer wields a gunblade which he calls "Hyperion". His Limit Break, Fire Cross, allows him to use an attack called No Mercy. He later uses the more powerful techniques Demon Slice and Bloodfest against the player. Seifer has a short temper and is often depicted as a bully who desires attention. He is also fiercely independent and is often punished for his recklessness. He is the leader of Balamb Garden's disciplinary committee with his friends Fujin and Raijin. After joining Ultimecia, he becomes the leader of the Galbadian army.

During the introduction sequence, Seifer cuts Squall across the left side of his face with his gunblade, leaving a scar. Squall retaliates with a backhand slash that leaves Seifer with a mirrored scar. At the following field exam in Dollet, Seifer acts independently from his teammates Squall and Zell, abandoning them; consequently, he fails and is not promoted to SeeD. Spurred by dreams of a brighter future, he defects to Sorceress Edea so he could be her "knight". From his point of view, Squall and the others are "evil" and he recognizes himself as a hero. As Seifer is brainwashed by the sorceress, he alienates himself from his friends. Eventually, Fujin and Raijin abandon him and he is defeated shortly afterward. Following Edea's defeat, the party confronts Seifer one last time as he now serves Ultimecia, and either they or Gilgamesh defeat him. Seifer escapes, kidnapping Rinoa and bringing her to Adel. At the end of the game, Seifer is seen fishing and having fun with Fujin and Raijin.

Nomura had originally intended Seifer not only as Squall's rival, but also as part of the love triangle between him, Squall, and Rinoa. Although this concept was shelved in the final script, Seifer remains Squall's rival and his appearance was designed to contrast with Squall's. They have equivalent but mirrored scars on their faces and their jackets are of opposing colors and lengths. Both characters use gunblades; Squall's gunblade is larger and requires two hands, while Seifer's gunblade is lighter and can be wielded with one hand. A younger version of Seifer makes an appearance in Kingdom Hearts II as a member of the Twilight Town Disciplinary Committee with Fujin and Raijin. Seifer in the virtual Twilight Town is a rival of the main character, Roxas, and at one point mentions that he does not wish to cooperate with destiny. He is voiced by Takehito Koyasu and Will Friedle in the Japanese and English versions, respectively. He is also featured in the rhythm game Theatrhythm Final Fantasy as a sub-character representing Final Fantasy VIII.

The book "Converging Traditions in the Digital Moving Image: Architectures of Illusion, Images of Truth" discusses that while Seifer is seen as a show-off and a troublemaker, protagonist Squall Leonhart identifies with him. IGN listed Seifer as the 91st best video game villain, stating that he makes for a great rival due to the similarities between him and Squall.