Mecha-Ude: Mechanical Arms

Hikaru Amatsuga is a middle school student who lives in Kita-Kagami City and one day, he hears cries for help and finds a mechanical lifeform in the shape of an arm named Alma. Before he knew it, Alma ended up connecting (derizing) to his hoodie. Hikaru is unable to abandon Alma, so the two end up working together. But then, a mysterious Mecha-Ude user confronts them.

The Mecha-Ude user Aki Murasame transfers into Hikaru's class with the intention to secure Alma. She belongs to an organization named ARMS and she starts following Hikaru and Alma around 24/7 and Hikaru seems completely exhausted because of all of this. Meanwhile, a huge company named the Kagami Group that is taking away the consciousness of Mecha-Udes and using them as weapons starts targeti...

Hikaru and Alma are taken to ARMS HQ. There, Hikaru is told that he is not suited to be a Mecha-Ude user, and Alma falls under ARMS' protection. Meanwhile, multiple incidents where Mecha-Udes are forcibly ripped away from their users occur. Aki goes to check on these incidents and Hikaru and Alma end up accompanying her, but...

Hikaru was dealing with the fact that he had to still go to school while learning to live with Alma, working as a member of ARMS, and being followed around by Aki.

Aki is finally able to track down the worm-type Mecha-Ude user who killed her family. But the person she finds is her younger twin sister Fubuki, who should've also died in the incident that killed Aki's family. Aki is told the truth about what happened in that incident during her unexpected reunion with Fubuki and she's informed of one other cruel truth.