The Tree of Life is a safe haven where animals from everywhere come to heal or if they are of an endangered species. Rafiki told the Lion Guard about it near the end of Battle for the Pride Lands. They hope to receive help for problems for which they can't find any solutions elsewhere. The Tree of Life has all kinds of animal habitats.
The Tree of Life appears to have mystical powers, as Queen Janna channeled its energy to help heal Ono's eyes to restore his vision. This power appears to have limits however, as Janna could not restore Ono's vision to be as keen as it used to be.
After Kion and Ono get workplace injuries during the final battle against Scar, Rafiki advises that they and the rest of the Lion Guard set off to find the Tree of Life to find the cures for their conditions. It is vital for Kion to find this tree because it's the only place he can find a treatment for the effects of Ushari's venom, which got into his left eye when he got his own scar.
Bunga causes a rockslide that blocks the main entrance to the Tree of Life. Rani gets worried that the visitors might be a threat, so Ullu leads the Night Pride to the Guard. Rani and Surak think that they are strangers; Baliyo, Rani's younger brother, goes up to see who the strangers are. After hearing Kion say that nothing will stop his group from getting to the Tree of Life, he gets the wrong impression and attacks the Lion Guard, along with the rest of the Night Pride. Kion uses the Roar of the Elders on Baliyo, and Rani gets upset. She says that he and his friends aren't welcome at the Tree of Life, and later asks if her brother is okay, and he says that he was. He starts to feel dizzy while Rani decides to speak with her grandmother, Janna. Her grandmother says that the Roar has returned to the Tree of Life. Rani asks about the scar in Kion's eye, and Janna explains. She tells her to remember Sisi Ni Sawa. She proceeds to tell her granddaughter to welcome the Lion Guard to the Tree of Life. After speaking to her Night Pride, they all think that the Guard shouldn't come in. Rani then talks to her parents, Sãhasí and Ãnanda, to get advice. She is worried that something bad will happen if she lets the Lion Guard in, but they say to listen to Janna and welcome the Guard into the Tree of Life. After finding the Guard they notice that they cleared the path without trying to enter any further. Kion apologizes about the rockslide and says that he and Ono needed to be healed. Rani soon welcomes them to the Tree of Life.
Rani brings the Lion Guard inside the Tree of Life to speak with her grandmother Janna. The queen asks Nirmala to help heal Kion's scar, and while Kion is getting healed, Janna asks Rani to show the rest of the Guard around the Tree of Life. Rani tells them all about the Tree of Life and says that everyone is welcome, as long as they respect the Circle of Life. Ullu comes to tell Rani some important news, and Rani leaves the Guard behind. They soon meet Makucha, Chuluun, and Ora. The Night Pride fights them off, but Kion and the Lion Guard arrive after it's all over and crashes into the Night Pride. Rani doesn't want their help and asks them to leave as soon as possible. After hearing the descriptions of the animals the Night Pride fought, Kion realizes that Makucha and the others must have followed them. This greatly angers Rani, as this confirmed her worst fears about something bad happening if she let the Lion Guard into the Tree of Life, as there is now a group of vicious predators on her doorstep. Rani talks to her grandmother about this problem and claims that they should have never let Kion and the Lion Guard in. Janna tells Kion to not worry about protecting the Tree of Life and to continue his healing, and Rani asks Nirmala if Kion is healed yet. She says that she is just like him. Makucha and the others come back again and the Night Pride fights them; Baliyo gets bitten by and is left incapacitated. Kion completes his task of getting the flower and helps fight off Makucha and Chuluun. Rani then thanks the Lion Guard for their help.
Rani is hanging out with the Lion Guard and her brother. Soon, Kion and Nirmala come along, Kion has mud on his face. Nirmala says it's part of his healing. Nirmala then says that Kion has a long way to go before he gets healed. She also says that it's time for Ono to be healed, and Ono is excited and he heads off to the Tree of Life. Fuli asks if Bunga can be any noisier when he eats. Baliyo says that Bunga should meet his friend Binga. Rani and her Night Pride soon see Mama Binturong being chased by Makucha's Army, not realizing that Mama being attacked was all an act so that she could enter the Tree of Life without raising suspicion. They save Mama and welcome her to the Tree of Life. Kion asks if Rani is here for Ono's healing, and Rani says that she's just letting Mama Binturong (calling herself Granny Ginterbong as an alias) into the Tree of Life. After Mama Binturong finds out the weaknesses of the Night Pride and Queen Janna, Rani takes her to a nice place to get some rest, but Mama dismisses her, telling Rani to get some rest. The Night Pride hears that Makucha's Army is attacking Mama Binturong, but that is actually a decoy because Mama Binturong is on the other side of the Tree of Life so that Makucha's Army could attack Queen Janna undeterred. The plan goes awry and the Night Pride spots Mama Binturong after failing to attack Bunga, and she claims she was attacked by Binga and Bunga. Bunga explains what really happened and she runs off as Bunga explains who she really is. Before she goes off too far, Bunga and Binga stop her with their stink. Rani tells Ono that he was the one who figured out Mama Binturong's plan and thanks Ono for his help.
While all the other members of the Guard are off doing their own things, Beshte goes walking around the Tree of Life to sightsee. He meets a polar bear, some penguins, and other amazing animals. However, the animals think that Beshte is a threat. They called him Poa the Destroyer. After Beshte saves Pinguino's life, Beshte is called Poa the Life Saver.
The Night Pride and the Lion Guard are stopping Makucha's Army from preventing a family of tigers from entering the Tree of Life. Makucha's Army is forced to retreat and Rani invites the tigers to see Queen Janna. Ullu soon comes by, saying that Queen Janna would like to see her and the Night Pride, along with Kion. Rani sees a group of animals surrounding the Tree of Life, and Rani realizes that Janna is dying. Baliyo doesn't want to go in, but Rani and the Night Pride offer him emotional support. Queen Janna weakly says her goodbyes to her family and tells Rani that it's time for her to become queen. Rani thinks she isn't ready, and Queen Janna says she is, and that she has everything she needs to help her. Rani starts to cry as Queen Janna passes away. Kion gives Rani his condolences and Rani thanks him while crying on his shoulder as Kion sheds a tear as well. Makini soon tells the animals of the Tree of Life the sad news. At the funeral, Rani is sad and alone so Kion goes to talk to her. Rani talks about her admiration for her grandmother and is worried she won't measure up to her. Kion encourages her and opens up about his own doubts when he started leading the Lion Guard. Kion tells her that he hasn't been talking to his grandfather Mufasa since he got his scar, out of worry that he'll resemble Scar to Mufasa. Rani says they all have scars while showing him the scar on her forepaw while saying Sisi Ni Sawa, which is what her grandmother said that convinced Rani to let Kion into the Tree of Life, which is a decision Rani is now glad about. Rani tells Kion that just talking to Mufasa might make him feel better and Kion thanks her for the advice, while telling Rani she's a lot like her grandmother, leaving Rani taken aback by the favorable comparison. Makini soon shows Rani all the paintings that she made in the Tree of Life. The tigers soon come back and ask if they can stay at the Tree of Life; Rani says they're welcomed and goes with Bunga to find them a new home. Kion goes to speak to his grandfather, and Rani goes to her coronation at sunset. Fuli, Anga, and Nirmala greets Rani with a song as she becomes queen. All the animals cheer for her, while Makini declares it's time. Makini anoints Rani's forehead, saying Janna would've been proud of her before declaring Rani as the new queen of the Tree of Life, causing all to chant "Long live the Queen". That night, Rani tells her grandmother that she's ready to be queen.
Rani and the Night Pride are forced to fight with Makucha's Army at dawn, but the Night Pride is exhausted due to their normal patrol being almost over. Kion and the Lion Guard arrive to try and help fight off their enemies, but Kion's orders interfere with Rani's orders, which causes the Night Pride and Lion Guard to stumble and collide into each other. Rani takes full command and they manage to drive off Makucha's Army. Rani tells Kion to follow her lead from now on and that Kion has potential to be a great leader, which Fuli and Bunga dispute, saying that he already is a great leader. Despite being worried that he's not much a leader now when he can't control the Roar, Kion offers the Lion Guard to patrol during the day so that Rani and the Night Pride can rest, which Rani accepts. Fuli tells Rani that she's worried that Kion is getting worse because he now lacks confidence in himself, while Rani tells Fuli to have faith in Nirmala's healing. But, Rani privately tells the Night Pride she's worried that Fuli is right about Kion's healing progress. Rani goes to see Kion at the lake, and Kion is still worried that his scar won't ever heal, which means that he can't use the Roar and can't lead the Lion Guard. Fuli and Anga talk to Kion and help him remember a time when he was a lot younger. Kion finally learns that he's always been a leader. Makucha's Army comes back to attack at sunset, and Rani is the last to arrive. Since Rani hasn't arrived yet, Kion takes command and Rani is impressed when she makes it to the battle and witnesses Kion effectively leading the Lion Guard and Night Pride in coordinated attacks against the vicious predators. After the battle is won, Rani appears and tells Kion that he is a great leader.
Makucha's Army attacks at sunrise again when Rani and the Night Pride are exhausted from finishing their patrol. But Kion and the Lion Guard are well-rested and fight the predators. As Kion attacks Makucha, Rani is gazing at Kion in admiration. After the battle, Nirmala tells Kion that he should be healed now and the Lion Guard is excited to go home soon. But Rani is troubled by this and asks if Kion has to leave now. Kion eases her concerns since they still have to get rid of Makucha's Army. Rani is relieved by this and she and the Night Pride go get some rest. Bunga goes to the Tree of Life to speak to Rani, and disturbs her sleep. Bunga thinks there's something weird going on with Kion regarding his roar and Makini says that Kion is still working on his roar. Makini teaches Rani all about Askari, the first leader of the Lion Guard. She says that Askari would go to Cikha Escarpment to practice the Roar. Rani has an epiphany about Kion and the Roar, and she wants to see him alone, but Bunga insists on tagging along and she reluctantly brings him with her. They watch Kion using the Roar in different ways and are astonished. Soon, they hear about Makucha's Army attacking animals at the Tree of Life.
Anga brings them and Kion uses the full extent of his new roar abilities on them. He blasts them with concentrated bursts, creates twisters, and even summons lightning to save the Night Pride trapped behind a boulder in the Tree of Life. Everybody, including Rani, is amazed at Kion's new power and Kion roars a tornado that sweeps up every member of Makucha's Army and sends them all far away from the Tree of Life, ending their threat for good. After realizing the full power of Kion's Roar, Rani asks Kion to stick around instead of returning to the Pride Lands, which leaves Kion and the Lion Guard stunned.
After Kion is finished speaking to Mufasa, Rani comes up to Kion and asks if he's made his choice about staying at the Tree of Life. They both think that they make a great team and confess their feelings for each other, singing Of the Same Pride. Rani says that she could use Kion's help to maintain peace at the Tree of Life, which Kion says she doesn't need anyone's help with since she's already a great leader. Rani thanks Kion for the compliment and says that she wants to be a great queen as well and that a great queen could use a great king. She floats the idea of Kion being her king and mate. Before Kion can answer, the Guard arrives and they're wondering why they haven't departed yet. Rani wishes that they would consider staying and most of the Lion Guard is open to the idea except for Fuli who is reluctant. Soon, Azaad comes and Fuli asks how Rani knows him. She says that he's been to the Tree of Life before. She asks why he's here and he says that he was showing travelers how to get to the Tree of Life. Their friends, Janja and Jasiri, come and tell the guard that Zira and her pride have come into the Outlands. Kion knows that it's his duty to protect the Pride Lands from Zira, and decides to head back. Rani says goodbye to the Guard and tells Kion that she meant what she said, and Rani hopes that maybe the Roar will return to the Tree of Life again someday.
After relinquishing his title of the leader of the Lion Guard to Vitani and giving her the ability to use the Roar, Askari appears in the sky congratulating Kion for mastering the Roar. Kion is confused about why he still has the Roar and Askari tells him that there's another place that needs use of the Roar's help. Kion asks his Lion Guard if they would like to join him in protecting the Tree of Life as part of the Night Pride. They all say yes and head back to the Tree. With all of Kion's family and friends and other Pride Landers watching him, Kion becomes Queen Rani's mate and the Tree of Life's new King.