J-Team Precursors
Over the centuries, various groups of mostly young people in the main timeline have banded together in the name of learning, adventuring, and challenging a villain team or two. Many of them could be considered precursor groups to the currently-active J-Team, though they have all arisen independently much to people's knowledge. In the original timeline, traces of a J-Team-esque adventurer hero organization could be traced back to [Roman] times in the First Century. Despite following the same general tenets of the J-Team, the nature of these precursor groups and the level of organization they displayed varied considerably during their years of operation
The Omegas
Decried as bandits and thieves by the [Romans], the Omegas were a loosely affiliated group of insurgents that operated in [Roman]-controlled areas of the Ancient [Mediterranean] Basin. They often came from humble backgrounds; most of the members known came from peoples conquered and enslaved by the [Romans], plus a few [Roman] citizens sympathetic to their cause. While they lacked a true uniform, the Omegas are distinguished by their red cloaks and a common sigil on their shields and standards--the [Greek] letter omega. The Omegas were against chattel slavery and Pok´mon abuse. They were known to hijack slaver caravans, invade slaveholding estates, and interrupt gladiatorial matches specifically for this purpose. Their stance against slavery and the slaughter of Pokémon for entertainment in ampitheatres, however, meant that they were quite unpopular.
Much like the J-Team today, the Omegas have been known to run afoul of the Macraul Family, then a [Romanized] [Gaulish] gens who settled in other places across the Empire. One of the key leaders of the Omegas was a [Egyptian-Nubian] scholar based in [Alexandria], who was simply known by the Omegas as "The Physician."
The K-Team
The K-Team was a J-Team analogous group of young adventurers that operated between the late 1980s to the early 1990s. They were eventually responsible for the defeat of a villain group known as Team Fallout. Thus far, very little is known about their activities beyond that, and they have not been talked about as much since the 1990s.
Similarities and Differences
The J-Team emerged independently as an informal group of trainers who fought Missingno and 'M. Rather than directly building on these predecessors, they could instead be described as filling the same niche. They are unified by a call to adventure and by their tendencies to go against evils greater than most of their members could handle alone. What is known of the Omegas was they had some sort of de jure central leadership and acted for the most part like a militarized resistance group, whereas the J-Team was far less formally organized and has no military functions. The organizational structure of the /K-Team, if any, has fallen into obscurity. The public reaction to the J-Team compared to the others was also mixed. While the J-Team enjoy a mixed bag of popularity and have a loyal fanbase, the others did not fare as well. The Omegas championed moral causes that went against the societal values of their time and were villified. The K-Team did fight villainous teams in opposition to the status quo, but have become a largely forgotten relic of the Early 90s.
Possible Successors
In the Lillifuture, the paramilitary resistance group Team Signal has carried on the tradition once held by the J-Team of their timeline. Unlike the predecessors, who merely paralleled the J-Team's activities, the Signaljammers are far more deliberate in their imitation and are closer to an actual successor. Their end-goal is to keep the spirit of the team alive. Organization-wise, however, they are far more rigid in their structure and have a clear leadership under Dolly and the Benefactor.