Yuri, a 17-year-old high school girl, is suddenly transported to the Kingdom of Trizal, where a saint is promised to come from another world when the country is in danger. Yuri is perplexed, but Hamil, the priest in charge, tells her that as a saint, she must marry into the royal family and defeat the Demon King. But the prince she is to marry refuses to accept her? ...Fine, I'll defeat the Demon King on my own!