It was the April’s Fool and the twins were contemplating how they should prank their mother. Len suggested that one of them fakes their death and the other ‘finds the body’ and pretends to be all devastated in front of mom. Rin met the idea with enthusiasm and volunteered to play the dead twin.
Oh, what a show had Len put in front of his mother, crying and wailing over Rin’s ‘body’ all while he was laughing inside. But then he laughed aloud when he realized Rin was dead for real. This was her own ultimate prank on her twin.