Light Voice is featured in Azzanadra's Quest and City of Senntisten. It, alongside the Shadow Voice, appears to be a remnant of Sliske's psyche within the player's mind, after Sliske supposedly managed to transfer some of his essence into them during Sliske's Endgame. The Light Voice is pertaining some of Sliske's playfulness, being eerily positive and enthusiastic. As the Light Voice and Shadow Voice are within the player's mind, they only appear in the text box interface.
During Extinction, it is revealed that, at least according to Seren, the Light and Shadow voices are not Sliske but the faces of Guthix's enchantment that turned the player into the World Guardian.[1] The voices confirm Seren's theory during Twilight of the Gods. When the World Guardian asks why they look and sound like Sliske, they explain that this is the result of the adventurer absorbing both Guthix's light anima and Sliske's shadow anima, but they do not know why they don't resemble Guthix.
^Seren, "Extinction", RuneScape. "Seren: How curious. Do you know what they are? Player: No. Do you? Seren: Whatever Guthix did to you, those are the faces of it, it seems. Player: So it's not...Sliske? Seren: No. Not him. They are something else. Something more."
