User blog comment:IamJakuhoRaikoben/Chapter 492: Elder Sister and Younger Sister, Review./@comment-180.191.79.238-20160704235003/@comment-9595671-20160705180305

I think it's because Plutogrim was the result of Mard Geer using the Alegria spell to transform Cube, plus when you consider others could have been trapped in it before or even used to make the Cube...