Phantasy Star's greatest antagonist has always been something called Dark Falz or Dark Force, and PSO2 is no different, centering the game's story on this resurrected evil. In PSO2, Dark Falz comes in many forms and has a somewhat different background than in the RPG series for Sega consoles. However, they all have one thing in common -- a connection to the Profound Darkness, the main evil entity. While no trace of this villain has been seen in New Genesis just yet, it's possible there they are connected to the game's DOLLS enemies.
The Phantasy Star series dates back to the Sega Master System where the first game debuted. It was there the story of Dark Falz started and continued through most of the franchise's games. Its story has changed between the online and RPG games and it's likely New Genesis will stick to the same tale as the other online games, especially since it is connected to the original PSO2.
When Dark Falz first appeared in the original Phantasy Star, it wasn't revealed to be the true villain of the game until late in the story. It had come from another galaxy and possessed a king, who then became a tyrant and caused monsters to start appearing. In the end, the heroes are thought to have defeated Dark Falz, but it was merely dormant and reappeared in Phantasy Star II. This first appearance of Dark Falz was very basic, as there was only so much developers could do on old technology. However, its story was fleshed out over the course of the series.
PSII took place 1,000 years later, like PSO2 and New Genesis, and followed a descendant of the first game's protagonist. While the main enemy of this game is a computer entity known as Mother Brain, it may actually have been Dark Falz which caused it to be built in the first place. Like in PSO2: Episode 4, there is a crossover between Earth and the planet featured in the RPG series, Algo. Dark Falz is encountered on an earth ship orbiting Algo, which is also where Mother Brain operates. Earth was destroyed and when the earthmen discovered Algo, they destroyed it out of jealousy, which would be a bizarre move without the influence of Dark Falz. However, some Algonians fled on ships, which became the setting for Phantasy Star III.
While Phantasy Star III was very different in playstyle, Dark Falz was once again the main enemy. It jumped between ships, infecting people with its dark presence causing destruction and war. Two heroes eventually caught on to Dark Falz's plot and put an end to it, although like before it only lay dormant for 1000 years. The game goes through various generations of heroes defeating it over and over, and wasn't until Phantasy Star IV that the reason for its resurrection is revealed.
There, it was shown that Dark Falz was merely an extension of the Profound Darkness which was sealed away via three races from Algo. However, in PSIV, the seals have weakened to a severe degree, allowing the Profound Darkness to release more than one Dark Falz enemy, which the heroes must face. This is also the first time the story of two entities, the Great Light and Profound Darkness, being at odds with one another came about. At the end of PSIV, the Profound Darkness is vanquished forever. This ended the RPG series, but the online games carried on the tradition.
The Phantasy Star Online games kept the plot point of Dark Falz resurrecting every 1,000 years from its seal, and it also remained the main antagonist, with the exception of Phantasy Star Universe. However, it wasn't until PSO2 that the Profound Darkness made its reappearance and shares a similar story to the original games. In PSO2, an advanced race called Photoners discovered a sentient ocean planet with omniscient powers, Xion. They attempted to recreate it, but failed several times over.
One empty vessel, the closest to success, filled with the negative emotions of Photoners and became corrupted, birthing the Profound Darkness. It was at odds with Xion, seeking to destroy the universe while Xion sought to preserve it. Here, the Profound Darkness is more than alluded to infecting those under the burden of negative emotions, and it can even turn them into Dark Falz to serve it. At the end of PSO2, the truest version of the Profound Darkness is confronted, and it's revealed the player character is the Great Light sent to destroy it once and for all, thus connecting it to the other games.
So far, New Genesis has not mentioned Dark Falz or even Falzspawn. However, the game takes place 1,000 years after PSO2, which fits the timeline for its resurrection. The Profound Darkness never seems to be truly defeated, as its an evil entity. While at a glance, DOLLS don't appear to have a connection, they do have the photonic trait of being blue while calm, a natural photon state, and turning red when aggressive, a trait of Dark Falz photons. It's possible a resurrection is coming, but we won't know for sure until more of New Genesis' story releases.