devtrackers.gg
TL;DR: During the production of Arcane in 2017, Riot was not happy with the script and had to put a hold on Arcane. Since they had just hired a massive amount of top talented French animators, they needed something for Fortiche to work on and that's when Rise and K/DA Pops/Star were born.
First of all, if you haven't seen the short series "Arcane: Bridging the Rift", please go watch it. It's a series about the production and behind-the-scenes of Arcane. Extremely high-production and well-edited (seriously, they went so hard on this wtf).
In 2017, they had already wrapped up the production of episode 1 for Arcane. Christian, the producer and writer of Arcane, along with Riot built Fortiche up from a team of 5 people to a studio of 100 (now 300+) of top French animators to work on Arcane. However, Riot was not happy with the script for episodes 2 and 3 and decided to halt the entire production of Arcane for the follow-up episodes. If this went on, the massive team of animators they hired would not have work to do for months and would have to be let go. Christian felt the responsibility to keep the lights on at Fortiche, so he reached out to different teams at Riot to ask if they could have anything for Fortiche to work on. The outcome is 2 of the most watched music videos on the League of Legends YouTube channel, with Pop/Stars being #1 and Rise #3 (Warriors being #2, also animated by Fortiche).
We also got these absolute gems
https://imgur.com/a/nGhjdxT