Hero was a high schooler living an ordinary life.  One day, he meets a very strong and intelligent mechanical arm named "Mecha-ude". After a strange turn of events, the "Mecha-ude" started living inside Hero's hoodie and the two's life full of trouble begins.  As the boy and his "Mecha-ude" fights together and strengthen their bonds, the two also meets new friends who also fights along with each of their own unique "Mecha-ude" partners.  Out of those, one of the heroine has two "Mecha-ude" which appears out of her skirt. An active girl with a totally opposite characteristics from hero himself, he gradually becomes attracted to her.  But the two are confronted with other "Mecha-ude" users who are in search of the secret of "Mecha-ude" relentlessly.

Mecha-ude

Long ago, alien lifeforms came to Earth, fusing with people on the planet. Due to their appearance, they were dubbed "Mecha-ude," as when fused, they bore a striking resemblance to mechanized limbs.  Through an involuntary partnership, average middle schooler Hikaru Amatsuga works alongside the Mecha-ude Arma, who is an extremely rare and special existence. To protect Arma, the resistance group ARMS assigns the dual Mecha-ude user Aki Murasame to follow him wherever he goes. However, she is also looking for a mysterious Snake-Type Mecha-ude wielder, who has put many of her comrades in a critical state.  Behind the scenes, an organization known as the Kagami Group is searching for the mythical "Trigger Arm," a Mecha-ude said to grant unlimited power. When Aki's life is threatened by this group, Hikaru must team up with Arma to find the courage to fight back and, along the way, learn that his life will never be ordinary again.