The swords depicted in the anime and manga series "Demon Slayer: Kimetsu no Yaiba" are fictional and do not exist in reality. They are part of the creative world and imagination of the series' creator, Koyoharu Gotouge.

However, the design of the swords in "Demon Slayer" takes inspiration from traditional Japanese swords, particularly katana. The katana is a real type of sword that has a long and rich history in Japan. Katana and other traditional Japanese swords were used by samurai and have their own unique characteristics in terms of construction, design, and usage.

While the specific abilities and properties of the "Nichirin Blades" in "Demon Slayer" are fictional, the overall aesthetic and inspiration drawn from Japanese swords are based on real-world examples.