You can erase anything he cuts down, including concepts and beings. However, since Opponent is described as "The One Who Was Never Born," "less than nothing yet greater than all," it means that Opponent operates on a plane of existence that transcends even the ability to be erased. You's power relies on cutting down and erasing concepts, but Opponent's existence itself is an absence that cannot be interacted with or affected in the same manner. Therefore, Opponent’s nature as the ultimate transcendent entity makes You's erasure skills ineffective against him. Winner: Opponent