Personas is the manifestation of a person's heart and contain amazing powers.
Personas are a deep seeded power that lies in the heart of most people in the world. However, only specific people can use them after unlocking the power that resides in them. With the characters in Persona 3, they are able to use their Personas only in the Midnight Hour which puts them in the world of Shadows and can let them access their powers. In Persona 4, a character must overcome their own Shadow if they are to use their Personas. This requires being truthful with ones self as well as dealing with their own ego. Denying their Shadow will cause the Persona to mutate into a monster which must be defeated or else the person will die. After that, a character may use the power of Persona in the Midnight Channel.
Izanagi is the Persona of Yu Narukami and is a part of the Fool Arcana. Izanagi mainly uses lightning spells and physical augmented attacks in battle. Yu was able to summon Izanagi soon after he entered the Midnight Channel. Unlike most others that entered the Midnight Channel, he did not have to overcome his ego to unlock his Persona.
Jiraiya is the Persona of Yosuke Hanamura and is a part of the Magician Arcana. Jiraiya uses wind spells, minor healing spells, and magical defensive spells. Yosuke discovered Jiraiya when he encountered his own Shadow in a representation of Saki Konishi's family liquor store. It was here he ran into his shadow who claimed that living in Inaba was worthless and boring. When he denied that his darker ego was not a part of him, Jiraiya mutated into a monster. Souji was able to defeat the shadow and Yosuke gained the power of Jiraiya.
Tomoe Gozen is the Persona of Chie Satonaka and is a part of the Chariot Arcana. Tomoe uses ice spells, physical augmented attacks, and power up spells. Chie found Tomoe when the Investigation Team went to save Yukiko from her own castle. Instead, Chie found her own Shadow which told her how she really felt about Yukiko. Chie tried to deny it and like with Yosuke, Tomoe turned into a monster. Yosuke and Souji stopped it as Chie accepted the truth and gained the power of Tomoe.
Konohana Sakuya is the Persona of Yukiko Amagi and is a part of the Priestess Arcana. Konohana uses fire spells, healing magic, and defensive spells. Yukiko encountered Konohana when she was kidnapped and thrown into the Midnight Channel and found her Shadow in the castle that her conscience created. Her Shadow told her how much she hated that her future was already determined and she had to inherit the family in, something she denied as Konohana changed. Chie, Souji, and Yosuke saved her as Yukiko accepted her ego and gained Konohana Sakuya.
Take-Mikazuchi is the Persona of Kanji Tatsumi and is a part of the Emperor Arcana. Take-Mikazuchi uses lightning spells, heavy attacks, and physical power up spells. Kanji found the power of his Persona when he was kidnapped and thrown into the Midnight Channel, which took the shape of a male bathhouse. Kanji's Shadow mocks him for how shy he is around women and flaunts his supposed homosexuality. Kanji denies all of this, trying to be a man as his Take-Mikazuchi devolves into a monster like with the others. Yukiko, Chie, Yosuke, and Souji are able to stop the monster and save Kanji, who acknowledges that he might be gay but he's unsure. As a result, he gains the power of Take-Mikazuchi.
Himiko is the Persona of Rise Kujikawa and is a part of the Lovers Arcana. Unlike other Personas in the game, Himiko does not participate in battle. Instead, she stays on the sidelines and provides information about the dungeons and monsters the Team encounters. Rise finds her Shadow when she was kidnapped and thrown into the Midnight Channel, the area manifesting itself into a Gentlemen's Club. Rise's Shadow acts like a stereotypical lustful bimbo, something Rise denies as a pop star. Himiko transforms into a debauchery of herself as the Team tries to defeat it. It seems hopeless for a bit until Teddy uses his powers to defeat it. Rise comes to terms with what it means to be a pop idol and gain Himiko's power.
Kintoki Douji is the Persona of Teddy and is a part of the Star Arcana. He mainly uses ice spells, healing magic, and magical enhancements in battle. Teddy gained his Persona when Rise's dungeon began to crumble and Teddy's own Shadow appeared. Claiming that Teddy was a Shadow and nothing all together, Teddy denied him just as the others had denied the truth in their own hearts. As a result, a demonic monster that looked like Teddy appeared. When the group destroyed it, Teddy reluctantly accepted the truth that he was a Shadow and as through his admission, he gained Kintoki Douji.
Sukuna Hikona is the Persona of Naoto Shirogane and is a part of the Fortune Arcana. He focuses on light and dark magic and physical and magican enhancements in battle. Naoto knew she was going to be kidnapped and thrown into the Midnight Channel, knowing that the Investigation Team would save her. She encountered her Shadow in a Mad Scientists laboratory that represented her repressed childhood as her Shadow claimed to hate being considered a child and wanted Naoto to express her feminine side, surprising everyone since they all thought she was a boy. Naoto rejected her Shadow as Sukuna transformed into a monster. With the help of the group, Naoto understands that some consider her a child and accepts her Shadow, gaining the power of Sukuna Hikona.