Demon King from Today!

Flushed Into an Alternate World! (1x1)

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Yuuri Shibuya, after helping out another student who was getting picked on ended up getting flushed down a toilet to another world. After meeting Adelbert, he finds out that he is the new Maou (demon king). Conrad comes and saves him, taking him back to a nearby village where he meets Gunter. Here, he learns more about where he is and what the Maou is.