|“||They're toys though...||”|
After Kurumi was infected, Rii-san had placed the handcuffs on Kurumi's left arm and leg, attached to the sofa's legs as an added precaution. Yuki had taken these off of her before confirming her recovery, however, this only happened in the manga adaption.
Later, in chapter 44, Kurumi was seen equipping the handcuffs as an added precaution. These handcuffs were later discovered by Yuki in chapter 49, who assumed that she was captured but quickly realizes that she was only trying to protect them.