Reborn as the Dragon King

True prince declared heir, ceremony in seven days. King adopted antagonist, who believed throne was his. Upon his return, all power belongs to him, including Leona (Elven King's bloodline) who loves him and is to marry him, not the antagonist. Antagonist murders him, impersonates him for ceremony. Reincarnates as an egg, acquiring 'Phantasm Fear System'. To stop antagonist, he must create fear to gain points, evolve to human form rapidly within seven days.