Ai just loves her big brother, Yuzuru. He's so kind, so reliable and so cool! He always protects Ai from trouble and when she cries, he cheers her up! He's the perfect big brother. But, bad things happen soon. Her parents divorce and she and her brother are separated. Now, after nine years, one day, Ai, now 14 years old, finds a tall boy in front of her school. Who is this boy?