Warning: The following contains spoilers for One-Punch Man by ONE and Yusuke Murata, available now through Viz Media.
One-Punch Man Season 2 is now over two years old, but there are no official announcements for when the next season will begin. This probably has to do with the fact that the manga is still in the middle of its current arc. Despite this, it wouldn't be far-fetched to assume that the anime staff could potentially start another 12-episode season (or one cour). With what's been provided by the manga, there's more than enough source material for the production staff to make a Season 3 of One Punch Man.
Needless to say, it's important to remember where Season 2 left off. This ends with Saitama destroying Elder Centipede, an event that takes place around Chapter 85 of the manga, which dates all the way back to December 2017. Over 60 new chapters have been released since then. All this is covered within the ongoing Monster Association Arc. While this arc is not yet fully concluded, trying to adapt over 60 chapters into 12 episodes would be asking too much. The best course of action would be to divide up the current story arc into no less than 24 episodes (about two cours). Only one cour of the Monster Association Arc can be told right now, but that's all there needs to be.
The current Monster Association Arc, as its name suggests, deals with the Hero Association performing a raid on the Monster Association's base of operations. They do so in an effort to rescue Waganma, the son of a wealthy benefactor of the Hero Association, who is being held hostage by the monsters. The result is an all-out, earth-shattering war between the two sides, all of which takes place in Z-city, Saitama's hometown. The Caped Baldy therefore gets involved to complain about the noise. Part of the reason there's no Season 3 yet may have to do with said main character being a footnote for most of this arc.
Not only will the heroes have to go through hoards of monsters to save the child, but they will also need to face off against the Monster Association's Dragon-level leaders -- a series of one-on-one fights between the S-Class heroes and the Executives. This is great because it gives a chance for all the S-Class heroes who had minimal roles in the previous arcs to show off what they're truly capable of when using their full potential. Many of these heroes will likely become new fan-favorites by the end of Season 3.
Running parallel to the hero-monster war is Garou's story. In the anime, he is last seen being carried back to the Monster Association Headquarters by Phoenix Man with serious injuries. Garou will be pitted against heroes and Monsters alike, as he doesn't necessarily side with either of them. The Hero Hunter is determined to prove his worth and show what it truly means to be a monster.
Season 3 will likely end with the fight between Saitama and Monster King Orochi. The Caped Baldy will have to file one more complaint as he confronts his noisy neighbor directly. Since this neighbor happens to also be the Boss of the Monster Association, this should be an entertaining interaction. It would also make a perfect ending point for Season 3, as it features the main character fighting a primary antagonist of the arc. This epic battle perfectly encapsulates the blend of amazing visuals, action and comedy that One-Punch Man is known for.
If the anime ends up going past this point for whatever reason, here are some more available plot points that can be covered. Tatsumaki gets into an even bigger fight with the true mastermind of the Monster Association. Garou continues to mutate into an increasingly powerful threat. The S-Class heroes must work together to fend off the Executives of the Monster Association. While all this would be best saved for Season 4 and beyond, it could all very well take place sometime in Season 3.
Whenever Season 3 comes out, it's going to blow audiences away with everything that happens. However, it's important to keep in mind that Saitama will have a significantly reduced role in the story -- albeit to better show off the best qualities of other characters like the S-Class Heroes and Garou. Besides, if Saitama had more of a role, the season would be done in one episode, which certainly wouldn't be worth the two-years-and-counting wait. Like waiting for Saitama to show up, Season 3 should be well worth it.
