"Johari no Kagami" is a crystal mirror which is said in Japanese Buddhism to be used by Enma (the King of Hell) for inquiring into if the dead were right-minded or not before its death.
浄玻璃鏡（じょうはりのかがみ）は、（日本の）地獄(仏教)の閻魔が亡者の善悪を見極めるのに用いる水晶製の鏡。