Haruka, who has never been with a boy, suddenly got a "big brother" after her mother remarried! Haruka's father died when she was 4, so her mother had raised her alone for 13 years, until her mother remarried a man who worked in the trading business. Now Haruka has a new brother Ki who just came back from the U.S. and spoke fluent English. In addition, he was as handsome as a model, so she was very excited and nervous. This relationship between "siblings" who are not blood-related could be a little dangerous? (Source: Kodansha, translated)