After Kion discovers his new destiny as leader of the Lion Guard after experiencing the Roar of the Elders for the first time, he assembles his friends Bunga, Fuli, Beshte, and Ono to be a part of his team, but his father King Simba did not approve of his decision leaving his son downcast that his father doesn't see that he is taking his new role and responsibilities seriously.

As soon as Kion wanders off on his own he discovers a magical portal that leads him to a new world where magical ponies that include unicorns, pegasi, and earth ponies exist in with his best friend Bunga tagging along for the ride. There they meet Twilight Sparkle, the protégé of Princess Celestia, who arrives in Ponyville to prepare the Summer Sun Celebration. There they would also meet Applejack, Rainbow Dash, Rarity, Fluttershy, and Pinkie Pie along the way.

However, a new threat is on the rise as Nightmare Moon, the villianous mare from a book Twilight has read about prepares to plunge Equestria into an Eternal Night as she abducts Bunga. Seeing the world and his friend in danger, Twilight and Kion together, along with their companions journey to the old Castle in the Everfree Forest to find the Elements of Harmony in order to stop her as Kion attempts to prove to his father that he is worthy of his position as the Lion Guard's fiercest, rescue his friend, and help Twilight save Equestria.