From MangaHelpers:

Rio always wanted to be a model, but she was too shy to go to the audition alone. Instead, she took her sister Yui with her, and Yui is the one who became a popular model. Rio does her best to be proud of her little sister, and not be jealous about the situation. She even asks boys out for Yui, so that Yui won't be faced with potential rejection. One day, a pair of hot brothers, Sei and Kou, move into the neighborhood. Rio asks both of them out for Yui, but they both reject Yui through Rio. This dual rejection brings out clearly both Yui's selfishness and Rio's suppressed jealousy. What will happen next for Yui, Rio and their love lives? [tethysdust]