Yukio mixed a diuretic obtained online into a drink and gave it to his mother, Sachiko, while he himself retreated to the toilet. This was his method of making his mother urinate outside. Yukio's twisted desire to see his mother urinating drove him to drug his own mother. Eventually, as Yukio had planned, Sachiko went out into the garden. The sight of the golden arc shooting from Sachiko's crotch, which he had dreamed of, was incredibly erotic and sent Yukio further into a frenzy.
