Light orbs are a powerful source of power that exist in Hikarizaka and the Illusionary World. They are created whenever Tomoya, or possibly any person, helps someone else achieve happiness by completing a goal. They are also a powerful force collectively, and can cause miracles to occur.
Everything has its limitations, however, and the light orbs are no exception. The orbs have to follow three rules in the anime:
- The Light orbs will only do exactly what's asked, nothing more, nothing less. In the flashback arc when Misae asks Katsuki to love her forever, he turns back into his original form, which is a cat. Katsuki then follows Misae around in this form. Had Misae known that Katsuki was a cat she probably could have asked that Katsuki love her forever as a human. The need for specificity when wishing also manifests itself when Tomoya asks for Nagisa and Ushio to return to life. The orbs grant his wish, but to do it they bring him all the way back to the time that Nagisa gave birth to Ushio, leaving him with a set of memories of the previous timeline.
- Wishes are only granted if they're genuinely wanted. Katsuki can't use his wish to get the rain to stop falling on him, because it was not a genuine wish from his heart. The first time that Nagisa died, Tomoya, who had a chance to bring his wife back from the dead, (who has a second chance later on) instead wished that he had never met Nagisa. The wish wasn't granted because it wasn't a genuine desire in Tomoya's heart.
- Children are the culmination of their parents' hopes and dreams. This is something openly discussed throughout the anime. Ushio was able to grant Tomoya a wish because she is the culmination of the light orbs that he had collected and shared with Nagisa.