In the L&L AU, Chase and Elaine are twins and Trace is one of their childhood friends. The trio are all two years younger than the Red/Green/Yellow group and are the same age as Leaf, their other childhood friend. Growing up, Leaf, Elaine and Chase especially used to get into a lot of trouble, even breaking the law sometimes with stunts like trespassing and petty thievery. As time passed however, Elaine began to distance herself from such shenanigans and spend more time with the more dutiful Trace. When the time came for them all to leave Pallet for their pokémon journeys, Elaine and Trace chose to head out on their own as rivals rather than deal with whatever scheme Chase and Leaf were likely to come up with this time. And boy did those two have a scheme.
Leaf had heard rumors that Team Rocket wasn’t as defeated as everyone thought they were and she and Chase decided to investigate this for themselves. While Elaine and Trace’s journey was very similar to the plot of the Let’s Go games, just with much less Team Rocket influence (so a basic journey around Kanto challenging gyms), Leaf and Chase were busy poking their heads into the criminal underworld. The two eventually do find Team Rocket by tracking down one of their secret bases. When they get caught by a grunt, however, Chase claims that they were interested in joining the team, hoping that would get them out of trouble. Instead, the grunt takes them seriously and brings the two young teens straight to Archer who figures they show enough promise to be able to start on some low-level grunt work.
Now rather in over their heads, Chase and Leaf have no choice but to go along with their orders, which is mostly just busywork as they’re still kids. While both are initially working together in what is essentially a gofer position, eventually Leaf discovers something unexpected – her grandfather, Blaine’s, name on one of the documents belonging to a scientist. Intruiged, she’s able to arrange a transfer to be a scientist assistant instead, and starts on a journey to discover the truth behind Mewtwo and her grandfather’s involvement in the project.
Chase, meanwhile, keeps at his grunt work, eventually getting promoted to field work, which is where he first meets Mondo, a character who appears in one of the radio dramas as the supplier to the Jessie, James and Meowth trio while they’re in Kanto. Over time, Chase and Mondo got assigned to more missions together as they were both too young to do any real criminal work, eventually being promoted to the communications department. Unlike Leaf, who leaves the team after achieving her goals surrounding Mewtwo, Chase remains a member of Team Rocket, eventually becoming a field agent with Mondo as his contact back on base. The two end up dating, eventually getting married and adopting a son, Hunter, together.
Elaine meanwhile, returned home to Pallet with Trace once the two managed to defeat the Elite Four and Champion, entering the Hall of Fame. Not long after, she learned about how her brother had gotten involved with something sketchy. She contacted him to try and urge him to leave this path behind, but Chase’s mind was set. He liked this job and found it way more fun than just being a regular trainer. The relationship between the twins never fully deteriorates, but they do have a slightly strained relationship just due to their different outlook on things, especially since Elaine eventually joins the Indigo Elite Four. Luckily, by that point, Silver has taken over Team Rocket and reformed it somewhat, so Elaine and Chase don’t have to worry as much about meeting as enemies down the line.
And what of Trace? He becomes an elementary schoolteacher in Pallet! He and Elaine are married with two daughters, Raine and Scout, and he finds the whole sibling rivalry pretty overwhelming, though he finds out on the rare family reunions that he and Mondo actually get along quite well, all things considered.
Pokémon Legends & Legacies 