|First appearance||Successor of the Earth|
|Appears in||Successor of the Earth|
|Relations||Saki Amamiya (father; status unknown)|
Airan Jo (mother; status unknown)
Commander Deko (nemesis; dead)
|Race||Human (with Achi's blood)|
Isa Jo is the male protagonist in Sin & Punishment: Star Successor.
Isa is a human from Earth 4 and the son of Saki Amamiya and Airan Jo, the protagonists from Sin & Punishment: Successor of the Earth. He was present when Saki attacked New York City, as is made clear by the events of Stage 6 in Successor of the Earth. Little is known of his life between then and the events of Sin & Punishment: Star Successor. Prior to Star Successor, Isa trained on Earth 5 with Deko. He apparently showed an extraordinary amount of skill in combat; Hibaru even says that he used to fight Deko to a draw in sparring. Because of his exceptional strength, the Creators gave him the mission of traveling to Earth 4 and killing Kachi. Once he met Kachi, however, he befriended her and tried to help her escape. While attempting to escape, the two of them were pursued by the Nebulox and their army, who were assigned by the Creators to succeed where Isa failed. After Deko managed to incapacitate Kachi at the end of Stage 6, Isa attempted to save her by carrying her out of the volcano, but was struck with a large piece of lava. Falling into the sea of lava surrounding Mt. Fuji, he finally awakened the full extent of the powers he inherited from Saki, transforming into a powerful titan. He stored Kachi within his body to protect her and so that she would keep him sane, just as Saki had done with Airan at the end of Successor of the Earth. With these powers, he laid waste to the NS, defeated the Nebulox, and killed Deko. He and Kachi returned to Earth 4 afterward; their status since is unknown.
Being the son of Saki, Isa inherited the powers Saki obtained from Achi. This gives him potentially immense powers, enough to singlehandedly defeat five god-like entities and ravage a planet-destroying machine. The only apparent downside to these abilities is that, like his father before him, he cannot retain sanity on his own while transformed. Like Saki, he must store his companion, Kachi, inside his body, or else he will become a mindless killing machine.
In his transformed state, he is armed with two weapons. One is a large cannon that functions the same way as his Cannon Sword, but without a blade. Instead of slashing enemies with this weapon, for his melee attacks, Isa simply smashes this weapon into his enemies, delivering devastating blunt-force trauma. The other is a weapon that functions similarly to Kachi's gun, but this weapon has three long, claw-like blades attached that he can use to slash enemies. In Isa & Kachi mode, Isa can switch between these two weapons, just as the player could switch between Isa and Kachi prior to the third phase of the battle with Deko. In this form, Isa also has no need for a levitation unit, as he can naturally levitate and fly while transformed.
- "Your face isn't that bad. And your fashion sense is certainly...interesting."
- — Hibaru Yaju
In his human form, Isa has similar physical characteristics to his father, Saki. Their faces are somewhat similar, and both share the same hair color. Isa wears a partially-unzipped blue vest and short, brown shorts. He wears long, black and white gloves, and tall, white boots that reach halfway up his thighs, most likely part of some sort of military uniform. He wears a soccer ball-like module on his back that allows him to levitate, functioning in the same way for him as Kachi's hoverboard does for her.
Transformed, Isa's appearance changes dramatically. He takes on the form of a humanoid titan, barely resembling his human form. His face turns a dark grey, almost black, and his eyes turn completely blue. His hair grows long and turns white, and his torso turns orange, white, and black. His arms and legs turn white as well, and his fingers extend and grow long, black claws. His lower half no longer looks organic, and in fact looks mechanical. His legs swell and become rather blocky, and a growth forms around his waist, somewhat resembling a utility belt. His feet appear nearly unusable, as they appear fused to his legs.