Magic Stone Gourmet ~I Became the Strongest by Eating the Power of Monsters!~ (Web Novel)

Thanks to a goddess, the protagonist reincarnated as a noble. Initially things went smoothly, but his skill, "Poison Decomposition EX," was so underwhelming that he was ridiculed at home. However, one day he discovers he can eat monster magic stones to absorb their abilities and learns he's the prince of a neighboring country! In the royal palace, he finds an environment where he can experiment, train, and unlock his full potential with abundant magic stones. He even manages to obtain the abilities of the legendary monster, Durahan! Surrounded by a proactive fiancée and a clumsy female knight, the boy's new life as a "king" begins! Note: The perspective shifts from first-person to third-person partway through the story. The web novel version is significantly different from the book version and the manga adaptation.