Nanami Haruke is a famous composer, where her name is known through the country; Japan. The cause of her fame is due to a prestigious and successful group that had their debut not too long ago. The mentioned cluster are colleagues of Nanami Haruka. So they would expect they knew a majority about her life. However, what if Nanami had an elder sibling she never mentioned? Well, it's a female to be exact. So technically a sister, older sister. As any older sibling would be, she is protective of Nanami who is constantly surrounded by her male acquaintances. Which leads to tension between the individual and the cluster that's in the entertainment industry. .... Heh. Let's see how this goes.