yandere living armor story where a human is abducted from Earth by a gigantic alien spaceship one night via tractor beam. Once on board they find out the ship is a massive coliseum-style fighting arena that travels the galaxy kidnapping members of various alien species and making them fight to the death. As one of the galaxy's squishier races the human is put into a suit of artificially intelligent armor, that's programmed with combat knowledge and the goal of keeping its host alive at all costs, and then the human is assigned to a team and put through a grueling training regimen for weeks. The human bonds with their teammates during training and learns to put up with the sardonic quips of their armor, which speaks to them in their head through neural link.
Then the televised fights begin, transmitted to trillions around the galaxy. The human is woefully unequipped for the brutality of the arena games, and survive mostly by surrendering to the armor and letting it control their body like a puppet as it fights off various monsters. But they get better and better as they continue to fight and train, and soon they're able to make the basic moves unassisted, which is good because each fight is more difficult than the last. The human's friends among their teammates are almost killed on several occasions, and the human has to fight against the armor's control in order to come to their rescue, because the armor is only programmed to care about its host's survival, not anyone else's. but the armor is smart and self-learning, and it learns to understand the human's motives and starts working with them to keep their teammates alive, not against them. The teammates survive, and they improve in working together, all of them, and they keep surviving. They move up through the ranks of the games.
The armor continues learning about its host's personality, and decides the human is too soft-hearted to survive long-term, but they don't deserve to die, so it hatches a plan. It continues working with its host to win games until the next time the massive spaceship is docked above a planet, and then it orchestrates a jailbreak. It jumps onto one of the deadly lasers and points it at the arena's armored outer wall and burns a hole through it, and then it starts escaping, punching through wall after wall of the spaceship's labyrinthine corridors with its human limply along for the ride. They make their way to the control room, defeating every guard and officer in their way, and destroy the control-boards, disabling the ship's security systems and freeing everyone on board. Then they make their way to the escape pods, and ride one down to the planet's surface.
Once on the planet they settle into a new routine of living, much too far away from Earth to ever make it back. The human takes up a job as a courier, running errands for townspeople in the city where they settle, and through trial and error they learn which alien foods they can digest and which they can't. The armor purrs with delight whenever the human wears it, which is always on the job as it lets them sprint faster through the streets. The armor is positively in love with its host, and resolves to protect them for the rest of their life, no matter what.
But the owner of the arena spaceship, who survived the jailbreak attack, has rich and powerful friends amongst the galaxy's elite, and the resources to continually send goons down onto the planet to search for the human and recover them and the armor dead or alive. As the human works to save up enough for space passage to another planet they're continually attacked by bounty hunters and other henchmen, and the armor becomes increasingly paranoid about its host's safety with each attack. Soon the armor locks down around its host, refusing to come off for any reason, and it starts threatening their kindly neighbors to root out possible informants. And it becomes increasingly brutal during its fights with their enemies, killing them all and uncaring when collateral casualties pile up. The human has no control over their body, the armor an expert at puppeteering them now and unwilling to relinquish control, convinced it knows best how to protect them. And its fighting prowess is certainly nothing to sneeze at. But as the bodies pile up around them the human being finds themselves in a nightmare they're unable to wake up from, and their only hope of salvation is to find a way to escape the planet for the great unknown of space...
