Two girls with completely different personalities are forced to become roommates due to a misunderstanding. From initial antagonism to later inseparable companionship, they gradually become each other's most important people throughout their long youth. The favoritism hidden in their companionship, the unspoken dependence, and the increasingly out-of-control emotions slowly cause their originally simple friendship to cross boundaries. Years later, when youth has ended, she finally understands— Some people, once they enter your life, can never be replaced by anyone else.