Magic Stone Gourmet: Eating Magical Power Made Me the Strongest Volume 4 (Light Novel) by Ryou Yuuki

Ein’s headed off to the Adventurer’s Town Barth for more info on the red foxes! Alongside his beloved advisor, the prince leaves to scope out the nearby Demon Castle. However, the boy quickly learns that his fox hunt is about to get rocky when a series of earthquakes shakes up his plans. In the hubbub, a primordial beast suddenly rears its head and it’s starving to exact revenge against the crown prince and royal family! If the first king couldn’t slay this ancient monster, what hope does Ein have? And just what is lurking within the shadows of the Demon Castle? The crown prince’s journey is nowhere near its end—it’s just getting started.