Basi is a large, bulky gray hippopotamus. He has some gray spots on his back, and a pale gray underbelly, which also extends under his chin. His toes are a distinct brown. He has several large black whiskers, and three brown hairs sticking up from his head. He has a notch in one ear, with three smaller hairs sticking out from within the pink inner ear. His eyes are teal.
Basi is a wise hippopotamus, who shares many words of wisdom with the members of the Lion Guard. Much like his son, he has a very friendly disposition, and is quick to forgive Makuu despite all of the problems he caused. He also seems to be extremely indefatigable and persistent about what he does even if he's hurt. Also, much like Kion's father, Simba, Basi is very encouraging and supportive of his son, who he has tremendous pride and faith in.
Basi is first seen at home, in Big Springs. Noticing his son taking a bath in the springs, he explains that when there are too many fish in the lake, the crocodiles come along and eat the fish, completing the Circle of Life. Pua then arrives and asks Basi if the fish are ready. Basi explains that while there are more than last time, there are still not enough for him and his fleet. He invites them to return next week, and Pua agrees. One crocodile by the name of Makuu, however, is not happy when Pua tells them to move on. Makuu feels that Pua is weak for not ignoring the hippo's words, and challenges him to a Mashindano. When Beshte asks his father what the mashindano is, Basi explains that it is a fight that determines the leader of the crocodiles. Pua accepts Makuu's challenge, and the event is held later that evening.
Basi, along with many other hippos, travels to the location of the Mashindano, witnessing the battle between Pua and Makuu. He explains how the fight will work for the youngsters. Makuu eventually manages to win and, defeated, Pua leaves, as Basi explains that the loser is banished from the Crocodile Float. However, the win soon becomes a problem, as Makuu pushes Basi and his herd out from Big Springs, forcing them into the elephants' Watering Hole.
After Kion manages to get Makuu to return to the Crocodile Float, Basi is pleased to see that everything has returned to normal, watching Makuu's Float leave Big Springs. As a way of making peace with the new leader, Basi calls out to Makuu before he leaves, telling him that when there are enough fish, the crocodiles are welcome back if they ask.
Basi is seen practicing singing for the Kupatana Celebration with Zazu listening and acting as conductor. The Lion Guard and Simba watch from a distance as Basi sings. Simba then compliments Basi's skills to his son Beshte.
Basi later performs at the Kupatana Celebration along with Mbuni the ostrich, Muhanga the aardvark, an elephant, and Twiga the giraffe. During the fight, he is seen staring angrily at the jackal pups after his son knocks them down.
Basi and his son Beshte are in the Flood Plains, walking through the reeds and stomping them down. Basi explains to his son how making the Hippo Lanes after a big rainstorm has been a hippo tradition for a long time. He goes on to say that the lanes help others cross the Flood Plains, and that a good Hippo Lane must be "straight and true" and that someday, it will be Beshte's turn to make the lanes.
Suddenly, a voice calls out for help. The pair rushes towards the sound of the voice and locates Young Rhino, who is trapped in the reeds. Nearby, Makuu and another crocodile are lurking, positive they won't find him in the mess. However, Beshte bursts through the reeds and warns him to back off, reminding him that the Flood Plains are a safe spot after a rainstorm. Makuu challenges Beshte, believing him to be outnumbered. Basi soon arrives and chastises him, and Makuu slinks away, muttering angrily that hippos always follow the rules.
Confirming they're gone, Young Rhino explains how he was trying to cross when he became ensnarled in the reeds and mud. Basi comments that he should have waited, but Young Rhino claims that he was in a hurry, but soon admits that he should have waited. Basi and Beshte start to untangle him, but a flock of egrets startles him greatly, and he accidentally thrusts his horn against Basi's leg. Young Rhino is freed regardless, and he thanks them, promising that he'll wait. Basi assures him that it won't belong.
Bunga, Fuli, and Kion approach their friend, stating that they heard an animal call for help. Fuli adds that it took them forever to get through the muck, but Beshte proudly tells them what happened. Bunga is impressed, suggesting that Basi should join the Lion Guard. However, Basi is instead reminded that he needs to complete the Hippo Lanes and starts to move away. He stumbles on his injured leg, though is persistent in his desire to continue. Bunga tells him not to worry since the Flood Plains will dry up soon, though almost immediately after the group hear the rumble of thunder in the distance. Basi finally hands the job over to Beshte, who isn't sure he is capable just yet. When Basi assures him that he knows he can do it, Kion also reminds him that he is the strongest in the Pride Lands and that they all believe in him. Beshte finally agrees to take responsibility for the new lanes. Sensing their presence will slow him down, Kion, Bunga, and Fuli offer to take Basi to high ground where he can rest.
They soon reach a large rock where Basi can rest. After thanking them, Basi is certain that staying off it will help to heal it quickly. Suddenly, Ono swoops down to alert them to a problem. He tries to tell them of the other rainstorm, but the Guard already know. Ono continues to explain that the Sable Antelopes' grazing grounds were already flooded out in the rainstorm yesterday, leaving them nothing to eat. But since they're too stubborn to move and are still standing around in knee deep water, they'll likely be completely underwater by the next storm. Basi suggests leading them there, but Ono informs him that the herd is on the other side of the Flood Plains. But Basi reminds him that, by the time they return, Beshte will be done with the Hippo Lanes. The Guard thank him for his suggestion, but Basi only wishes he could help his son. Bunga assures him that Beshte will be fine, and the Lion Guard race off.
Much later, a second storm breaks out. With Beshte erroneously making the Hippo Lanes completely wonky and labyrinthine, he returns to his father to inform him of his mistake, adding that he let him down. Basi refutes his claim, stating that he was the one who let him down. He tries to stand, but his injury is still hindering him. Beshte rushes to support his father, and Basi proclaims that the two can work together to make Hippo Lanes large enough for the entire herd to move through. Beshte is immediately cheered up, and the two get to work.
Halfway across the Flood Plains, Basi halts suddenly. Beshte asks if he's okay, to which he replies that he just needs to rest. He assures his son that he will be right behind him, urging him to finish. Beshte agrees to go ahead, promising he'll make him proud. When he races off ahead, Basi exclaims that he always makes him proud, before relaxing in the rising water. However, just behind him, Makuu emerges with more of his float members, commenting that getting rid of the hippo means that he'll have control of the Flood Plains.
As Basi raises himself, he decides that it's time to continue helping Beshte, but hears Makuu behind him. The crocodile states that he's the guest of honor for their meal plan and starts to approach. Beshte arrives just in time, but Makuu is unhindered by his arrival since they're crocodiles and they outnumber them four to two. Basi is sure they can handle them, but Beshte knows his father is still hurt. When the crocodiles start to approach from many angles and Makuu claims they have nowhere to run, Beshte states that they need a new lane, urging his father to follow him. They turn around and exit through the reeds, but Makuu's float takes pursuit.
Basi questions what his son is doing, reminding him that the lanes must be straight and true. But Beshte explains that it's not happening this time, and leads him around. Makuu's float continues following until they stop at a junction having heard a noise. They turn around to see Bupu's Herd charging down the lane, and Makuu calls for his float to dive. They do so but get trampled by the sable antelopes. Basi then compliments his son, and the pair approach Makuu. Beshte reprimands him for his actions and orders him to use the new lanes to get out while his father watches the crocodiles angrily. Makuu groans, but succumbs to the hippo's orders.
Later, Basi and Beshte watch the animals move through the newly formed Hippo Lane. The rest of the Lion Guard approach the parent and child, complimenting them on their work. Even Ono admits that Beshte was good at making them after all. Beshte thanks Ono for his words and Basi ends the conversation by saying that he never had any doubt, smiling proudly towards his son.
Along with several other Pride Landers, Basi takes part in a Christmas celebration for Timon and Pumbaa. He and many other Pride Landers spend all day rehearsing and almost leave until they discover the reason for Bunga's determination in creating the perfect display.