The Kumbuka celebration is meant to honor Simba's victory over Scar and subsequent succession of the throne of the Pride Lands. The ceremony takes place at Pride Rock, where the Pride Landers gather to pay homage to the royal family. Rafiki presides over the celebration.
The Lion Guard discusses the Kumbuka celebration in the Lair of the Lion Guard, where Bunga tries to attribute Scar's defeat to his uncles, Timon and Pumbaa. However, the other Guard members and Makini explain that Simba fought a great battle against Scar and took his rightful place as the king of the Pride Lands. Thus, the Kumbuka celebration began.
Later on, the Pride Landers come to celebrate at Pride Rock. In the midst of the celebration, Simba is stung by Sumu the scorpion, and the Kumbuka celebration is broken up.