TLDR: What if Gege loved Mechamaru and was hugged as a child?

Heavenly Restrictions. Sometimes they suck, sometimes they're awesome.

Kokichi Muta was one such person who wielded a heavenly restriction. His body was broken down, unusable, and in exchange, he was given an amount of cursed energy that surpassed nearly everyone else. He was also given a massive range, covering the entire country, from which to use his puppet manipulation. His genius mind invented countless robots through which he could experience the world around him, all while his body suffered.

He had worked for Kenjaku and Mahito as a spy in Jujustu High, all so that he could obtain a normal body, allowing him to enjoy life alongside his friends.

That was the knowledge Kenjaku had of him. He was a fearsome threat, and almost definitely had a secret weapon, but even a special grade automata could be handled by Mahito and Kenjaku.

There was one factor Kenjaku didn't account for.

It wasn't some giant mechanical foe that Mahito faced, as Kenjaku was somewhat expecting, but a small, humanoid one. No... power armor?

Mahito sensed a soul inside, and it didn't matter then. He dashed forward, imbuing extra energy into his technique as to go through the armor straight to the body.

It failed. The soul shifted, and the body held no response. Instead, it summoned a blade from within its arm, and in one swift strike, severed the head of the cursed spirit in both body and soul.

Several years ago, a man died. A man whose body was recovered by Jujutsu Society, along with his weapons, and sealed away for research. A man that Kokichi had managed to take himself.

Kenjaku was stunned. This was unlike anything he'd ever seen before. Toji Fushiguro wasn't alive, but he wasn't dead either; he was a puppet, a component in a mechanical soldier beyond sorcerers.

After a long, drawn out fight, Mechamaru Mode: Apollyon had defeated its opponents.

Mode: Apollyon

Apollyon is the result of Toji Fushiuguro's corpse being a reanimated vessel to Mechamaru's powers. Two opposite heavenly restrictions combined into one, this behemoth is easily special-grade level.

Its physical strength and speed surpass Fushiguro's by a strong margin, as it wields both the powers of his own body, and its exterior armor, which allows it to use reinforcement to further amplify its power with Grade 1 levels of strength.

Apollyon's left arm is a prosthesis created by Mechamaru as the primary point of its technological power. Due to his failure to evade Hollow Purple, Toji's arm was gone, and the prosthesis replaced it. It has several combat functions, including potent blasts, weaponry, and even the Inverted Spear of Heaven alongside the Thousand Mile Chain.

His nervous system is controlled via a technique reversal of Kokichi's puppet manipulation, Neural Path, allowing him to puppet and reanimate a corpse so long as it wears his modifications. This allows him to output its sensory information to his mind directly, and control it as if it were his own body. The brain and spinal chord have been augmented to also function far beyond what normally was possible, processing data much faster and surpassing bodily limits when necessary, much like a Sandevistan from Cyberpunk. Its senses include both Toji's immensely powerful superhuman senses, and numerous sensory devices. This includes 360*, thermal, electromagnetic, and night vision.

Through its augments and armor, Apollyon can also fly with thrusters at high speeds, resist powerful attacks, and can even receive healing through reverse cursed technique.

While Heavenly Restriction can sometimes change, Kokichi's was unchanged after his alteration by Mahito. This is because his restriction's drawback occurred at the beginning of his life, rather than constantly like Toji's. He had already paid the price of his power. Thus, in this universe, Kokichi manages to get his dream body, while maintaining special-grade power through Apollyon (much to Gojo Satoru's dismay).