Milim who was a big fan of One Piece, decided ask rimuru to create the One Piece world and decided to go there with her fellow demon lords! How would octagram fit in in this world that full of pirates and monsters??

3 years after the defeat of Yuuki... In this timeline, Rimuru is bored and getting increasingly impatient. In a hope to satisfy this eternal boredom, he ends up, with the help of Ciel-sensei, dimension-hopping into the world of Demon Slayer. How will things play out in this new world and how will the story of Demon Slayer change? (Rimuru is very heavily nerfed, at least for now). *I DO NOT own Demon Slayer or That Time I Got Reincarnated as a Slime. The characters and plot that are depicted in this story either belong to Koyoharu Gotouge, or Fuse. All art in this story also belongs to its respective owners and I do not own them in the slightest.

A bored Rimuru Tempest accompanies Diablo when he goes to meet with an old friend in the Netherworld. What will happen when he meets an out-of-place human boy who piques his interest? (Tensei Shitara Slime Datta Ken and Mairimashita Iruma-kun crossover)