I'm a High Schooler, But I Became an Owner of a Castle in Another World

Hiroto Kiyokawa is a completely ordinary high school freshman - but that's until he gets sucked into another world by the power of a mysterious old map! As the so-called Diferente - a savior from another world - the lord who summoned him commands him to rid their world of vampires. But Hiroto chooses another option - he plans to start a country where different races like vampires and mummies can coexist!

(Source: Manga Planet)