Taehyun Choi lives with his sister, Hakyung Choi. You could say they lead a normal life. On one hand, Hakyung has a good job and is successful; however, Taehyun is not good at studying. His life changes drastically when he accidentally discovers that he and Hakyung are not siblings. This leads him to decide to confront her, but she then suffers a serious accident and loses her memory. This is where everything changes, as those feelings of kinship will become much more significant.