Nuka is a scraggly lion with brown fur, with grey fur on his mouth and underbelly, red eyes and a scrawly black budding mane, goatee and elbow fur. His whiskers are bent in a few places on either side. His inner ears are a darker brown with a tuft of black fur sticking out from each.
Nuka is very hot-headed, and leaps into fights constantly underestimating his opponent. He is somewhat cowardly at times, leaping high into the air when he is caught off guard. Nuka is constantly trying to get on his mother's good side, even though he is not above disobeying her words if he decides that his way is better. Nuka is also seemingly disgusted at the idea of lions working alongside hyenas.
Prior to The Lion Guard
Nuka, along with his siblings and mother used to be a part of Simba's Pride during Scar's rule. After Scar was defeated by his nephew Simba, his mother, Zira could not accept Simba as the true king. She struck out and attacked him and, as a result, she and her family were banished to the Outlands.
When Jasiri leads Kion to the watering hole that was stolen from her clan, she is ambushed by Nuka, who pounces and pins her down. He scolds her for returning, but before he can attack, Kion pounces on him and pins him down instead. His brother, Kovu approaches, and Nuka orders Kion to let him go, since the fight was now two against one. Jasiri then joins Kion, making the fight equal. They circle around each other, and Nuka voices his disgust in a lion that sides with a hyena. Kion questions what they're doing in the Outlands, and Nuka scoffs at the idea that they'd be welcome in the Pride Lands. Kion assures him that his father would be okay with that and, after Nuka asks who his father is, Jasiri reveals it to be Simba, the Ruler of the Pride Lands. Nuka is shocked, but when his little brother gets excited at the prospect of returning and seeing Kiara, he agrees with his brother on taking him back to see his mother. Nuka leads them all away.
When they reach the watering hole, Kovu introduces Kion to his mother, Zira, and his sister, Vitani, whilst Nuka complains that they pounced on him. Zira is certain that he pounced first, and he admits to doing so. Nuka waits for his mother, who discovers that Kion is the leader of the Lion Guard. She explains Kion's special power briefly. She manages to get Kion to give a demonstration of the Roar of the Elders in a way Kion did not believe was possible whilst Nuka watches with awe. Kion is eventually persuaded to speak with Zira alone, leaving her children with Jasiri. Nuka growls towards her, but Zira calls for him to play nice. When she's gone, Jasiri snaps towards Nuka, scaring him and hides behind his younger brother and sister.
A while later, Nuka becomes antsy waiting for his mother. He leaps down from some rocks and attempts to attack Jasiri, but Kovu steps between the pair, urging his brother not to start anything. Jasiri laughs, telling him that any game Nuka can play, she can play better. Nuka comments that he's not playing and races towards her, but his mother returns just before he can attack. Surprised by his mother appearing, Nuka swears that they're just playing, and tries to put his paw around Jasiri's shoulder, but she shrugs him away and makes him fall so she can speak with Zira, where she informs her that Kion has decided to let the lions have the watering hole all to themselves. Nuka watches Jasiri leave.
His mother brings him to Kion, who she declares has chosen to side with the hyenas. Nuka then worriedly asks his mother if they should be concerned about his Roar, but Zira explains that if Kion uses it against lions, he'll lose it. And if he doesn't use it, they win regardless. This gives Nuka the energy he needs to strike Kion, and he lunges towards him. He strikes out, but Kion merely headbutts him back to his siblings, where Vitani shakes her head and utters his name disappointedly. Shortly after, the rest of the Lion Guard and Jasiri enter, tackling the Outsiders. Nuka tells his mother that he's scared, and backs away when the Lion Guard and Jasiri approach them. His mother tells them to stand tall, since they can take them.
Although Kion at first refuses to use his Roar, Bunga reminds him of the real reason why Scar lost his Roar was because he used it for evil. Kion remembers, and orders them to leave both the Pride Lands and the Outlands before using his Roar of the Elders to throw them over a wall and far, far away. When Nuka and most of the Outsiders arrive in a new area, Nuka gazes around with confusion and asks where they are. His mother replies that it is their new home.