Mecha-ude

A long time ago, alien life forms visited Earth and interbred with the local population. They were given the nickname "Mecha-ude" because of how they looked because, when united, they looked a lot like mechanized limbs. Hikaru Amatsuga, a typical middle school student, collaborates with the Mecha-ude Arma, an incredibly uncommon and unique being, through an unintentional partnership. The resistance organization ARMS assigns dual Mecha-ude user Aki Murasame to accompany Arma wherever he goes in order to protect him. She is also searching for a strange Snake-Type Mecha-ude wielding who has critically injured many of her allies. Behind the scenes, the Kagami Group is looking for the fabled "Trigger Arm," a Mecha-ude that is supposed to provide limitless strength. When Aki's life is in danger due to this group, Hikaru must work with Arma to muster the strength to defend himself while also realizing that his life will never be the same again.