One day, Hino Mariya, an ordinary office lady, casually bought a lottery ticket, won the grand prize, and suddenly became a millionaire! While dreamily thinking about how to spend her 300-million yen windfall, she accidentally dropped her bankbook. A beautiful girl named Tenma Tsujido happened to pick up the bankbook, and then asked Hino to become her sugar mommy in exchange for returning the bankbook...?