As dungeon-like treasure vaults started appearing throughout the land, more and more people began signing up as treasure hunters—risking their lives to obtain the vast riches and ancient relics inside. In the imperial capital of Zebrudia, the top hunter party is the Grieving Souls—a group of six childhood friends led by Krai Andrey, who is thought to be the strongest of them due to having a reputed wide array of skills. However, Krai actually has no special talent. His accomplishments are actually the result of his friends being overpowered. Krai has repeatedly attempted to leave the party out of fear his lack of aptitudes would one day cause his companions' downfall. Nevertheless, everyone around Krai thinks differently, making him feel obligated to remain the group's leader.

College student Tokiwa gets invited to a mixer by his female classmate Suo. But when he arrives with his friends, they're greeted by three dazzlingly handsome men?!

Hikaru Amatsuga's days of tranquility come to a sudden end when he rescues Alma, a mechanical arm crying for help. Alma fuses with his jacket, introducing Hikaru to the world of mechanical arms: mysterious, sentient weapons that normally become a part of their users' bodies. Forced to flee for his life, Hikaru is eventually captured by Aki Murasame, a twin mechanical arms user working for ARMS, an organization that protects the machines against unethical treatment. The Kagami Group, a nefarious organization that treats mechanical arms as mere tools, seeks to recover Alma. Hikaru is deemed a failure by ARMS for his lack of natural predisposition to be an mechanical arm wielder, so Aki is assigned to be his bodyguard. But Aki is defeated by Jun Kagami, who cruelly tears out her two mechanical limbs, condemning the girl to a slow death. Unwilling to abandon Aki to her grim fate, Hikaru miraculously awakens his power and neutralizes Kagami. Now a full member of ARMS, Hikaru is determined to unravel the truth about mechanical arms and protect his newfound friends and allies.

Noel longs to be a Seeker like his heroic grandfather, slaying the beasts that emerge from Abysses and exploring far-off lands. Unfortunately, it turns out he's nothing but a measly Talker–a job with no combat skills whatsoever. Undaunted, Noel sets out to establish the strongest clan in all the land, using his silver-tongued Talker skills to unite assassins and heroes under his leadership.