In Unitopia & The Nine Realms: The Rotten Egg, Buddy, an outcast unicorn hatched from a cracked egg with no Class or Realm to call his own, discovers he has the rare ability to travel freely between all Nine Realms. When Unitopia faces rising chaos after the shattering of the Lumina Core-a magical artifact that once sustained harmony-Buddy is chosen to recover its fragments and restore balance. Joined by Pepperminki, a spirited gummy creature, Buddy embarks on a perilous quest across the Realms, facing daunting trials, unraveling ancient secrets, and confronting his own self-doubt. As Buddy grows into his role as a Messenger, he learns that his differences make him uniquely suited to bridge the divisions between the Realms and combat the looming threat of the Shadowcorns.