[AyuHamasaki01]

^ True.

But she was also blindfolded in the scene where she, the sister and the brother-in-law where in the same room (and where she touched the man's shoulders).

here's another comment:

''The girl has a mental disability. She isn't blind but she pretends to be blind. The older sister awakens one night to see her younger sister touching her brother-in-law but never witnessed her younger sister hugging her. The younger sister wanders around the house, acting blind. The husband is understanding and sympathetic of this but her older sister does not like her younger sister touching her husband. The older sister stays up, waiting for her sister to come into the room like the previous night but the younger sister sees the light is on in the room so she does not come in. Instead, she sits in her sister's closet, feeling her clothing. The younger sister wants to be just like her older sister and sees her sister wearing makeup so she decides to put some on as well. During dinner, the older sister notices the makeup and believes her younger sister is trying to 'win over' her husband from what had happened. Out of jealousy and rage, she grabs her younger sister and proceeds to wash the makeup off violently. When it doesn't, she proceeds to 'drown' her sister. As her younger sister reaches out as the lyrics say 'It hurts, it hurts, unni.', the older sister realizes that all her younger sister wanted was to be just like her."