Flushed Into an Alternate World!

Yuuri Shibuya was just a normal Japanese high school kid who likes baseball and had a strong sense of justice until one day on his way home from school he sees a former classmate of his, Murata, being bullied. He steps in to try and stop the bullies but they just grab him instead and dunk his head in a toilet in the girl's bathroom. But for some reason, when his head enters the water, Yuuri is sucked into the toilet and ends up in another world. When he wakes in an unfamiliar area, he initially assumes that he is at a theme park because of the medieval-style clothes the people are wearing. He tries to talk to the villagers but they attack him. Adalbert von Grantz rides up on a horse and saves him from the villagers and uses some form of magic to unlock the local language hidden in Yuuri's soul. Conrad Weller then rides up and after a short fight Adalbert runs away. Conrad takes Yuuri to a small village where he meets Gunter von Christ who tells him that he is the new king the Demon Kingdom. They then take Yuuri to the castle where he meets Wolfram von Bielefelt and Gwendal von Voltaire, Conrad's two half brothers (who do not look anything alike!).