A sentient robotic arm living in your hoodie sounds absurd until you realize the show actually commits to it. The chemistry between Hero and Mecha-ude has the warmth of a buddy cop movie crammed into an OVA that refuses to waste a single frame on exposition. You get the action, the weird-as-hell premise played straight, and a kid learning that the strongest partnership isn't about power, it's about someone choosing to stay with you even when they could leave.

Hikaru Amatsuga leads an ordinary life until he crosses paths with Arma, a strong and intelligent Mecha-ude that ends up living inside his hoodie. Long ago, alien beings arrived on Earth and fused with people, taking a form that looks like mechanical limbs. Arma is an extremely rare one, and the partnership pulls Hikaru into constant trouble. To keep Arma safe, the resistance group ARMS sends Aki Murasame, a lively girl who wields two Mecha-ude, to stay at his side. Aki is also hunting a mysterious Snake-Type user who has badly hurt her comrades, and Hikaru gradually grows attracted to her. Meanwhile the Kagami Group searches for the legendary Trigger Arm, said to grant unlimited power, and when Aki is endangered, Hikaru must find the courage to fight alongside Arma. The result is a one-episode sci-fi action OVA built around mecha battles.