Flushed Into an Alternate World!

Yuri Shibuya was just a normal Japanese high school kid 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 girls' bathroom. Yuri is sucked into the toilet and ends up in another world. When he wakes in an unfamiliar area, Adalbert von Grantz unlocks the local language hidden in Yuri's soul. Conrad Weller then rides up and after a short fight Adalbert runs away. Conrad takes Yuri to a small village where he meets Günter von Christ who tells him that he is the new king of the Demon Kingdom. They then take Yuri to the castle where he meets Wolfram von Bielefelt and Gwendal von Voltaire, Conrad's two half-brothers (who do not look anything alike!).