Proto was a planned character in Yu-Gi-Oh! ZEXAL.
Described as "a mysterious young boy", he was planned to show up before Yuma after the conclusion of the war with the Barians and the disappearance of Nash, Rio, Astral and Don Thousand. Proto would have revealed a shocking truth behind the events of the anime to Yuma, telling him that a wicked power, the "Numbers", shouldn't exist in this world, then beginning a Duel against him. In the battle, he would have Summoned "SXyz" (
Proto would have used a Deck centered around "SXyz" monsters Summoned through Shining Xyz Evolution, in opposition to Chaos and Rank-Up Xyz Evolutions. He would have used very likely relative "Rank-Up-Magic" cards as well.
Proto is somewhat similar to the manga-only character Luna, in that both think that the "Numbers" are evil and want to wipe them from existence.