The Hidden Dungeon Only I Can Enter

Noir is the 3rd son of a poor noble and his job position is taken away by a more powerful noble. He also sadly lacks enough skills to attend the Hero Academy. He tries to find a way to be able to use his skill [Great Sage] better and stumbles across a hidden dungeon.

In order to find a way to earn enough money for the enrollment fee to the Hero Academy, Noir visits the Adventurers' Guild. However, the receptionist at the guild, Lola, doubts his skills, so he has to prove himself. Once she finds out he's telling the truth, she's supposed to offer him a reward, and...

Noir finds out the social ladder at the Hero Academy. A duke's daughter named Maria is the only one who gives him a helping hand. But he finds out that she has a curse that will kill her when she turns 16.

Right before his meeting with Luna, Noir goes to visit Olivia. He asks her if there's a more effective way to gain LP and she tells him about a forbidden skill that will make him very lucky in the most unexpected way.

In order to gain LP and money, Noir and the others enter a harem tournament. In this tournament, contestants show off their harems to be judged by a harsh crowd. Noir gets close with Emma, Lola, and Luna in order to try to impress the judges and win!

Noir successfully cures Maria's curse and receives a mountain of cash and decides to build a shop that sells rare materials, so he goes to the dungeon to gather said materials. He travels further down and meets a lion that apparently speaks human words.

Lola gets in an argument with a rival receptionist. Noir visits the Adventurers Guild and ends up getting caught in their fight. Noir decides to take down a dragon both for his test and for Lola, but...

Noir arrives at the 7th floor of the dungeon and he runs into a mysterious spirit who happens to look a lot like Emma when she was younger. Apparently, the spirit is having her life sucked away by something creepy and asks Noir to defeat it in exchange for a treasure.

Noir is invited to a high society party by Emma. The party is in a stir when thieves proclaim to visit it and steal away a few things that are there, but then Noir participates in a dance battle against a noble to win Emma's honor.

The day for the Hero Academy tradition, their trip to the hot springs, has finally arrived! The monsters they face on the way to the hot springs are tough, but the boys in the class who can't control their lust are a far bigger threat. What should Noir do to protect Emma and the other girls?

Noir opens his shop, Stardian Rarities. In gratitude, Noir tells Olivia he will free her from the Death Chains. Great Sage informs him a solution is on the dungeon's 15th floor, but a new threat shows up and forces them to take action.