Touru has found an unexpected new ally in the leader of the Thieves' Guild, Miri. With her coming along, Touru's party has grown again. However, despite his accomplishments in the Otherworld, an ominous shadow descends on his real life in Tachikawa. It seems his concerned coworkers have taken it upon themselves to check in on the wellbeing of their colleague, even if it means busting into his apartment to find out! Touru's other life is perilously close to exposure--will he be able to protect his Otherworldly secret?!

An underachiever’s quest for girls and glory at an apartment between worlds! There has to be a catch when a deluxe rental property is this cheap--and this one connects to a perilous dungeon in another world! Far from being dissuaded, Tooru jumps at the chance to sign the lease, hoping to go from high school dropout to big-time adventurer. He soon encounters a stranded knight: a gorgeous young woman named Ria. Tooru rescues her and takes her back to Earth, where she promptly mistakes him for a Great Sage, seeing normal things like running water for evidence of his powerful magic. Tooru may dreams of heroism, but first he has to figure out how to share an apartment with a cute girl from another world!

After getting into some trouble with the Mercenary Guild, Touru is whisked away by a hooded accomplice under a cloud of smoke. Even though he's been separated from Ria and Deet, they are reunited behind a hidden Iron Door, where there is safety from their pursuers. However, their saviors end up being members from the Thieves' Guild, and their actions weren't wholly benevolent--Touru and company have something they want!

Touru has scored a super-cheap cheap apartment in Tachikawa, Tokyo--because its front door opens into a classic fantasy dungeon. But the number of roommates keeps increasing. Now a rare white slime and a sexy elf have moved in!! As the first human to ever level up, Touru is planning a safer and easier way to grind more levels by breeding monsters, then defeating them remotely! But things get real as Touru ventures into the dungeon and saves a mage from a fiendish beast!

A stroke of inspiration in the mortal world has Touru and the others rushing back to the dungeon with a hot idea for rebuilding the Thieves' Guild's district. They want to plan a festival! Inspired by the summer festivals of Japan, Touru thinks a dungeon festival will be great advertisement for the Thieves' Guild. But in order to have authentic stalls, the adventurers need to go hunting--for rainbowfish! To make goldfish scoop special, it's time for one last adventure through the dungeon!

Touru's Tokyo apartment may lead to a dungeon in another world, but that doesn't mean he's strong enough to defeat the monsters lurking within it. So, through the power of modern science, Touru comes up with a risk-free Level-Up Plan, hoping to extend his life and become the Dungeon Master. But has someone else besides Touru made their way into the other world?!

After hearing the tragic story of how Ria lost her sword, Touru, Deet, and Shizuku hatch a plan to lure the adventurers who abandoned her down into the dungeon for payback! But this also leads to an incredible new discovery about the nature of Touru's apartment!