The Lost Ones are wanderers who come here from a distant world known as "Japan." No one knows how or why they leave their homes. The only thing that is certain is that they bring disaster and calamity. The duty of exterminating them without remorse falls to Menou, a young Executioner. When she meets Akari, it seems like just another job...until she discovers it's impossible to kill this girl! And when Menou begins to search for a way to defeat this immortality, Akari is more than happy to tag along! So begins a journey that will change Menou forever...
In a world, where the deities have descended from the heavens lies the town of Orario that features the Dungeon, which contains an assortment of monsters from goblins to dragons. Adventurers slay those monsters and take their shards, which are then used to craft magic items. To become an adventurer, people join groups called Familia. Each of which is named after and serves a resident deity. The adventurers and their attributes and abilities are ranked by level, improved by experience and supervised by their Familia's deity.
Bell Cranel, a novice adventurer, is the sole member of the Familia under the goddess Hestia. After being saved by top level adventurer Ais Wallenstein of the Loki Familia, he falls in love with her and decides to improve and become worthy of her attention. All the while mostly unaware that other girls, deities and mortals, also develop feelings for him. Especially Hestia herself.