The reason Roy chose to attack the third eye between Jubileus's forehead was that he knew that this eye was the manifestation of the divine artifact the Eyes of the World, and it was the source of her immense magic power.
Moreover, this eye should be an external object to her! After all, the original owner of the Eyes of the World was Archangel Aesir, and she was only using this divine artifact to make up for the loss of her original strength. Currently, Roy did not know what weaknesses she had, so choosing to attack this eye was the best choice.
However, Roy's sudden stab with sixty-four-fold strength failed to pierce this eye. When he was about half a meter away from the shining eye, an invisible force blocked the tip of Frostmourne. He gritted his teeth and increased his strength with all his might, but this invisible force barrier subtly maintained resistance equivalent to Roy's strength, preventing Frostmourne from advancing at all.
