|From Persona 2: Innocent Sin -|
Top: Maia's original form and Maia Prime
Bottom: Vulcanus's original form and Vulcanus Prime.
Prime Personas (called custom Personas in the PSX version of Persona 2: Eternal Punishment) are Personas that serve as stronger versions of their original incarnations with upgraded skills. The prerequisite to obtain these Personas are mostly story involved. In the Japanese version of Persona 2 and Persona 3, prime Personas are indicated by the suffix kai (改, lit. "modified").
Prime Personas are first introduced in Persona 2. Considered to be mid-game Personas, they are generous upgrades over their "previous" versions. Rhadamanthus Prime, Eros Prime and Maia Prime require the player to let the characters deal with their own problems in the scenario. If this has been done correctly, each of the characters will gain their prime Persona at the Mt. Iwato scenario while being able to keep their original ones. Vulcanus Prime requires the player to make all the correct choices for the previous three Prime Personas.
Exclusive to the PSP version, if the player did not obtain the prime Persona in this manner, they can mutate the initial Persona instead. This however, may prove difficult with Maia, as fusion spells that she can do often involve chance, or have negative effects, i.e. spells like Death's Roulette (which instantly kills one enemy or ally), potentially being very risky.
Persona 3 FES / Portable
Orpheus Telos is the only prime Persona in Persona 3 FES and Portable, and requires player to master all Social Links before fusing it. As opposed to Persona 2, Orpheus Telos is an end-game Persona. It resists every attack type and only possesses 1 skill (Victory Cry), allowing the player to customize the skill set on their own.