Finally having the once in a year summer break, Yumiko Fujimoto decided to fly back home to Japan from America to finally see her best friend, Yui Komori, again.
However, their reunion wouldn't last long because Yui will be living with her father's distant relatives while the man is away for a job overseas. Then one night, Yumiko couldn't stand her best friend's cries. She decided to accompany Yui on her trip to the place her Papa told her and she met the Sakamaki brothers...
At first, she was really annoyed at them while the guys are suspicious until Laito noticed what something is amiss about her. Turns out that she looked exactly like Subaru. But he's not just like a gender bend of her, but he's also her long lost twin brother and the keys hanging around their necks proves it.
Now being the sweet and caring little sister the brothers adore, what will happen if her dream of finally having a family turns into a forbidden love to win her heart? Will she be the reason they'll break apart? or will she bring peace to them?
And what about Yui? Will their friendship also break apart? And who is this mysterious person she always sees inside the mansion?
This a story of love, friendship, family and betrayal...