A college student buys a new apartment dirt cheap and the reason was that once the front door is opened from the inside it connect to a dungeon in another world instead so he goes to an adventure in the dungeon and meet new companions which treat him as a the Great Sage

All the Ore no Sora series deal with the Yasuda family. The first two series are about Yasuda Ippei. This is a Otoko Roman Manga and the genre is about Japanese men fantasizing about being successful in the world.

Rokudou is a loser, and everyone knows it. He gets picked on at school, gets snide looks from passersby, and can only muster up the courage to complain in secret with his equally hapless friends. Looking to turn his life around, he desperately uses an ancestral artifact passed down in his family for generations: a scroll that is capable of subduing all demons. However, in the modern age it has a different effect - it makes all bad girls fall in love with him.

An exterminator dies and finds himself in a fantasy world, without any skill with the sword or wand he carries on doing what he knows best.

Accidentally summoned by an ancient map, first year high school student, Kiyokawa Hiroto is forced by the arrogant Lord of the castle to exterminate the vampire that has been haunting his castle. Unexpectedly befriending a girl from Mummy tribe, Hiroto skillfully managed to capture the Vampire with her help. However, he is soon framed by the Lord of the castle. Bravely and kindly aiming to be a Lord, the fantasy of summoned to another world starts!

Ashida Mamoru is a god-tier manga assistant but his habit of turning authors lazy has left him without a job. Luckily one of his classmates from university happens to have a little sister who is a serialised manga author in need of an assistant.

University graduate Mu Siyun sent his resume to the star fleet on a whim and somehow became the Fleet Admiral! This is the story about an admiral with a harem of 3000 female soldiers conquering the universe.

Izumo Kunisaki, a descendant of Izumo no Okuni, is often mistaken for a girl. It is the bane of his existence. His father and best-friend often laugh about it. To top it off, he plays the girl roles in his family's Kabuki troupe. In this short, he discovers that that curse is also his greatest source of strength and will prove just how much of a man he is.

From MangaHelpers:
Hana, a high-schooler that is known as the cutest girl in school, gets pulled into a supernatural event while on a beach trip with her friends. This event, called a "Red Night Eve" involves a transformed extremely massive shark, which targets Hana while she's swimming! Luckily, she's rescued by the siblings Yayako and Yuuto Kagimori, students from her school who know all about these occurrences, and who even have a support program AI named Acacia in their tablet to help them. Not long after, Hana and the siblings are involved in another event, this time involving her precious class pet parakeet being transformed into something monstrous. With all these supernatural events, Hana's life is never going to be the same.

Keita Suminoe has two older (not blood-related) twin step-sisters who love him in a lustful way and have no problems expressing it. They even like to compete about it; much to the laughter of his friends (which he usually endures without problems). One day they come to his school to give him his lunch, resulting in him getting angry due to the atmosphere. To counteract his anger, they confess their tender feelings for him in front of everyone and leave. Feeling sorry he chases after them and says that he'll study hard in order to get in the same high school as them.

Takase is almost opposite of his brother weak and not good at school. He recently moved in at his brother's house, who is a married guy. He is placed under an exceptional coach to improve his physical health, and the coach also know as 'Venus of track' is none other than his sister in law. She is developing a new technique to improve body at a faster rate by management of testosterone levels in the body, in other words sexual desire management. She calls it 'absolutel obedience.' And Takase have to go under it to improve himself. This changes his life drastically, read and find out more.

The life of two slaves with their timid hero level master.

Third son of a "beggar noble" Nore lost his job and was at a loss. But as he was contemplating whether to become an adventurer fortune struck.

A Hidden Dungeon that no one knows how to get enter. A legendary place full of hidden things like extremely rare magical beasts, magic tools for gaining power and items that would be scarce all over the world. That's the kind of entrance that was opened.

"Without telling anyone about this place I'll secretly become the strongest."

This world is harsh to nobles of poverty. Without authority of honor, if I could at least acquire power――

A high school student Ichi who visited a ninja residence on a school excursion was caught in a strange structure during the tour and time slipped to the ninja world. Along with his friends, Ichi who got the “Ninpocho”, a key to return to the present age, returns safely to the present age. However, suddenly an awakening appears in front of Ichi who lives a peaceful life ...!?

Glas loses his path in life when he pulls a "flop" during his spirit summoning ceremony. However, he is given another chance when he receives a royal order to fight in the front lines, along with the Princess's knights, as a war doctor. With his "flop" capable of curing anything, the curtains unfold upon a new fantasy war chronicle!

Which one is the real you?! "Shota <=> Muscle Man" transformation harem comedy!
Highschooler Ryoutarou looks like a primary school boy, and all he wanted from his new school was to have a quiet and peaceful life. But on his first day in his new school the delinquent Mizuki calls him out and immediately destroys his dreams. Ryoutarou thinks he's in for a violent shakedown, but instead he's taken to a club room where girls with a certain sexual fetish gather....

Kein, a middle-aged adventurer, who while in the middle of herb gathering, found a rare item [Resurrection fruit].

Kein thought about selling it and turned it into money, but he met a girl seeking medicine to save her companion’s life.

She looked like Altena, his childhood friend who already died, he gave it in exchange for small change.

Actually, the girl was the strongest adventurer Anastrea, people called her the sword princess. The next day, Kein suddenly got an invitation to join an S rank party, beat down the strongest and the worst monster, miraculously gain lots of money, and finally get confessed by a 20 years old saint.

Kein’s simple life will change completely because of his encounter with Anastrea.

Tanaka is a middle-aged man with a face only a mother could love and a personality that no mother could love. After dying from an accident, a god sends him to another world where he has healing magic.

Join Tanaka as he goes around ogling beautiful women and then watching them get fucked by men other than him. This is a new manga version of the LN isekai series of the same name, so if you read the first series you sure as shit know what’s going to happen.

I fell into the reverse harem novel! I'm going to live here quietly, but my god. The villain and the red thread are twisted....life is twisted.

Former black company employee, Jiro Tanaka leaves his job due to overwork. In his home, he founds a job recruitment template which is from another world company. The job is to test the dungeon created by the demon king. There, the days of diving into the dungeon as a "dungeon tester" were waiting for him to complete the dungeon that even the hero would not be able to clear. He has a hot dark elf boss who has an amazing ability "Magic resistance". The New life of our MC starts!

by: Socialweebs