A side story of Dungeon ni Deai o Motomeru no wa Machigatte Iru Darou ka. It covers the story of the strongest 1st class adventurer "Sword Princess" Ais Wallenstein and her desire to reach even greater heights with her friends in the Loki Familia.

Bell Cranel is just trying to find his way in the world. Of course, in his case, the "world" is an enormous dungeon filled with monsters, below a city run by gods and goddesses who have way too much time on their hands. He's got big dreams but not much more when a roll on the random encounter table brings him face-to-face with the girl of his dreams--but what does a beginning adventurer have to offer a brilliant swordswoman? And what if the lonely goddess who sponsors his solo adventuring gets jealous...?! 
(Source: Yen Press)
 
Note: The manga got discontinued due to issues between the mangaka and the editorial.

Adventurer Bell Cranell's life changed forever when he met the goddess Hestia, becoming the first member of her familia. Since then, he’s gone on many adventures, growing much stronger in the process. But when he steps foot into Orario’s pleasure quarter, where Ishtar Familia reigns supreme, he soon finds himself in way over his head... With enemies all around him, he’ll need the help of a beautiful, fox-eared courtesan if he’s to have any hope of making it back home!
 
(Source: Yen Press)

Contrary to what the adventures of Bell and the Goddess Hestia might imply, not everyone goes into the dungeon of Orario to pick up girls. The veterans of the Goddess Loki’s Familia have lots of reasons for risking life and limb facing the monsters and mayhem lurking within the deadly labyrinth’s multiple levels, but new member and mage Lefiya just wants to prove that she’s worthy to be on the same team as her hero, the famed sword princess Ais Wallenstein. As for Ais herself, she’s seeking something that no one else even suspects, and she may find it when trouble comes after her from the previously unreached 59th level! 
 
(Source: Sentai Filmworks)

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