Purple Moon ga Kagayaku Yoru ni.

Every 100 years, the Purple Moon causes a miracle. "Be careful, of the Purple Moon that is coming in 3 days." After receiving such a warning from a stranger on the streets on her way to pay a surprise visit to her long-distance boyfriend, something incredible happens to Yuu, a high school girl who under her new unexpected circumstances can't go back home. Fortunately, Ryouya her dear boyfriend offers to let Yuu live with him till everything goes back to normal. Because everything will go back as it was before... right? (Source: MU)