Kion and his best friend Bunga are goofing around on Pride Rock, where Simba is teaching Kiara about life as a future monarch. Kion's antics with Bunga disturb the two, so they take their game away from Pride Rock and into the heart of the Pride Lands.
While playing, the two manage to lose their baobab ball in the Outlands. When Bunga goes to retrieve it, he is attacked by two hyenas, Cheezi and Chungu, who are under Janja's command. Before the hyenas can hurt Bunga, Kion steps in, roaring so loudly that the hyenas drop Bunga, who climbs to safety.
Meanwhile, Rafiki and Simba overhear Kion's roar, and the two come to realize that it is time for him to lead the Lion Guard. When Bunga and Kion return to Pride Rock, Rafiki leads them to the Lair of the Lion Guard, where he explains that Scar used to lead the Lion Guard until he lost his powers. Simba then tasks Kion with gathering a new Lion Guard to protect the Pride Lands.
Bunga and Kion set out right away, and Kion asks the honey badger if he will join the team. Bunga accepts, and his adopted uncles, Timon and Pumbaa, offer him enthusiastic congratulations. Unbeknownst to the friends, they have been spied on by Mzingo, a vulture minion of Janja's, who reports back to his leader about the newly formed Guard. When Janja hears the news, he announces to his clan that they will strike that very night.
On the other side of the savanna, Kion has appointed Beshte, Fuli, and Ono to positions on the Guard. He gathers the team together and attempts to show them the Roar of the Elders, but all that comes out is a squeak. Just then, Simba arrives and reacts in horror to Kion's choice of teammates. He insists that the Guard must be made of lions only and then berates Kion for treating his role as leader like a game.
Wanting to be alone, Kion isolates himself from his friends, where he encounters the ghost of his grandfather, Mufasa. The wise king tells Kion to trust his instincts and promises that he will always be there to guide him. No sooner has he faded from the sky when Kion hears Bunga calling for him, shouting that the hyenas are attacking a herd of gazelles. With no time to lose, Kion assembles the Lion Guard, using his paw to gift each of them with a special shoulder marking.
Together, the five friends attack the hyenas, driving them back into the Outlands. Kion finishes the fight with the powerful Roar of the Elders, and even Janja flees in terror. Simba happens to be watching from a nearby ridge and realizes that his son was wise to have chosen whom he chose. He congratulates his son on the victory and accepts this new, brilliant assembling of loyal animals.
Unlike his father Simba, Kion is a stickler for the rules. Even in the face of temptation - as seen when his baobab ball is lost in the Outlands - he heeds the words of his parents and intelligently recognizes the signs of potential danger. This strong sense of responsibility is in part why Kion has such a sturdy head on his shoulders and is much less likely to jump into dangerous situations than his best friend, Bunga.
However, despite this more accountable side, Kion is still a cub and enjoys a good tussle with his friends. He can be careless when it comes to games, as seen when he disrespects his father and sister during their morning lesson with his game of Baobab Ball. Though mature in aspects of obedience and rule-following, Kion is still young and doesn't recognize more adult concepts such as romance.
Though not well-versed in the adult sphere, Kion is strong-willed and able to trust his instincts, which is in part due to the gentle guidance of his grandfather, Mufasa. Undoubtedly, he is a cub who follows his heart, even in matters where those he loves oppose him, and is willing to follow the call of duty over pleasing family and friends.
His creativity knows no bounds, which is likely due to his straightforward nature and ability to see every side of a situation. This shines through most prominently when he is seeking members for the Lion Guard, for instead of simply following the path of duty and gathering a team according to tradition, Kion assesses all aspects of the job and picks the animals he feels are most qualified for the job. Even when his ideas are challenged, Kion is steadfast in his beliefs and brave enough to take a stand for what he feels is right.
Role in the series
Kion and the Lion Guard reprise their role in the series, becoming the main defense for the Pride Lands when his parents are off-world with The Jungle Crew. Though, in cartoon logic, he still retains his younger age after the second movie because he wasn't established with being older yet.
Spoiler alert: As of the most recent episode of The Lion Guard, however, Kion has become a young adult lion.