Historically, the boy only has appeared when there was imminent danger to his parents (3 times: beach, island, and in the sea god) . But they're in Elfhelm now, with no threat in sight, surrounded by the most powerful magic users alive. I wonder what that portends...
Would the Skull Knight and/or the gurus try something then? Maybe an attack in that "weakened" form? Revealing the boy's nature and prompting serious tension with Casca... And what would Guts do? Lots of possibilities...