During the fight with the demon, a ring suddenly appeared and release huge energy to defeat the demon. After healed by Grandpa Ginkgo, Prince of Ye found out he can saw the monster now.
It is because the demon realm crystal 
on the ring, which creates a barrier
لأنّ بلّورة عالم الشيطان في الخاتم
والتي تنشئ حاجزاً
Es liegt daran, dass der Kristall
aus dem Dämonenreich in dem Ring,
Eso es porque el Cristal
del Reino Demoníaco del anillo,
C’est parce que vous avez brisé
le cristal magique présent sur l’anneau
Perché il cristallo demoniaco sull'anello
É porque o cristal do reino demoníaco
no anel, que cria uma barreira
Всё из-за разрушенного барьера, 
который создавал кристалл