Since childhood, whenever office worker Kazuhiro Kitase slept, he would dream of a fantasy world. One day, he and his elf friend, Marie, lose an encounter with a dragon. Suddenly they wake up together in his apartment in Japan. Whenever Kazuhiro falls asleep or dies in the fantasy world, he and anyone he is touching are safely sent to Japan, and can return to the fantasy world by falling asleep. The pair start switching back and forth between touring modern Japan and going on fantasy quests, and eventually transport others to Japan with them. From Wikipedia

Given how half of the story could be called a ‘reverse isekai‘, where high fantasy characters are brought to Japan from their fantasy setting and are shown around by the protagonist, it comes as no surprise that much attention is called to real life locations being seen by the fantasy characters for the first time. Most of these points of interest are in central Tokyo or follow a trip to Aomori. Some fans of the light novel and manga were already interacting with the places depicted in Elf-san long before the 2025 anime aired, such as this ‘on-site’ cosplay shoot from 2023.

It took a some hard work to identify with some help from the Overpass Turbo Open Street Maps scripting language, but the library depicted starting in chapter 9 of the manga was clearly inspired by Tōyō Library in Koto, Tokyo. The circular sun room is a dead giveaway.