Yui was deeply devoted to her sister-in-law, Ai, treating her like a real sister. Whenever she had free time, she would visit Ai and her husband at their home, enjoying each other's company. Ai trusted Yui completely; they could talk about anything and even help each other out with secrets that nobody else knew about. One day, after Ai went through a painful breakup, Yui comforted her by accidentally kissing her. From there, their relationship changed drastically... As Ai continued to rely on Yui, their bond grew stronger than ever before.
