Prime Persona

Custom Personas are the Personas that specially customized by developer, they are stronger than their original incarnation with upgraded skills. The prerequisite to obtain these Personas are mostly story involved. In the Japanese version of Persona 2 and Persona 3, Custom Personas are indicated by the suffix "kai" (改, lit. modified).

Persona 2
Custom Persona is first introduced in Persona 2. They can be considered as mid-game Personas and are extremely useful for a long time.

Persona 2: Innocent Sin
There are 4 Custom Personas in this game, Rhadamanthys‎ Custom, Eros‎ Custom, Maia Custom and Vulcanus‎ Custom. The first 3 require player to make the right dialogue choices to overcome their users' weaknesses. When all 3 conditions are fulfilled, player will be granted the last Custom Persona which belongs to the protagonist after the Mount Iwato scenario.

Persona 2: Eternal Punishment
There is only 1 Custom Persona, Maia Custom, mutated from her original form. Maya must show Ulala compassion during the fitness club GOLD scenario to trigger the mutation.

Persona 3
Orpheus Telos is the only Custom Persona in Persona 3 FES and Persona 3 Portable which requires player to master all Social Link before fusing it. As opposed to Persona 2, Orpheus Telos is an end-game Persona and only possess 1 skill, leaving player to customize the skill set on their own. Since this Persona resist all kinds of attack type, making it the ideal Persona to conquer the game's ultimate boss without the trouble to changing between other Personas for resistance attributes.

Persona 4
Though named differently in Japanese and localized versions, Izanagi-no-Okami can be considered as the Custom form of Izanagi. It is only accessible in the first cycle by attending the True Ending scenario. From second cycle and on, player can fuse this Persona with all the required Personas.