An 18-year-old university student Takanori and 17-year-old high schooler Hikaru become brother and sister when their parents get married. Just when their happy family life is about to start their parents' plane crash on their honeymoon! Despite this， Takanori and Hikaru continue to live together. However， everything changes as they learn about the billion yen insurance money their parents left for them! An adventure full of comedy and romance is about to begin!