PersonaMost, if not all of the Persona in Persona 3 are based on folklore and mythology. Akihiko's two Persona are no exception. The rest of this section will explore the stories behind Polydeuces and Caesar and how they relate to Akihiko's character.
PolydeucesIn Greek and Roman mythology, Polydeuces (Pollux) is the twin brother of Castor. Both brothers are considered to be patrons of horses, however Polydeuces was more of a skilled boxer. Stories depict Polydeuces and Castor always being together. While there are variations of the their tale, the ending is typically agreed upon. While in the midst of battle, Castor is impaled by a spear right in front of Polydeuces' eyes. Polydeuces is a God and is thus immortal but his brother is not. Completely devastated by his brother's death, Polydeuces offers to go to Hades with his brother or share some of his immortality so they could still remain together. Zeus, however, chooses a third option. He puts the two brothers in the heavens where they become the major stars in the constellation Gemini.
Clearly the story of Polydeuces and Castor parallels with Akihiko and Shinjiro (Castor is Shinjiro's Persona). The two are not brothers by blood, but their relationship is so strong that they are described as being like brothers. Before Shinjiro's accident, they were inseparable. Shinjiro only joined SEES because he refused to let Akihiko be alone. Akihiko wouldn't take Shinjiro leaving as a permanent answer and consistently asks him to come back because he wants to be with him. Like Polydeuces, Akihiko is also a talented boxer. Akihiko experiences the same tragedy of seeing his beloved brother killed right before his eyes and grieves terribly. While Akihiko is clearly not immortal, Shinjiro's death while he lives on could still be representative of the story of Polydeuces and Castor.
In Persona 3: Official Design Works the designer comments that Polydeuces is a Spartan hero who is said to excel at boxing and can rival an entire army by himself. He is also said to be immortal because he has the blood of Zeus. It would seem, then, Akihiko's first Persona was definitely designed after the myth.