Warning: contains spoilers for chapter 155 of One-Punch Man
Recent chapters of One-Punch Man have seen some spectacular showdowns with phenomenally strong monsters, but one beast from the Monster Association has just achieved a scale that's almost unimaginable, as Evil Natural Water blends into the Pacific Ocean.
The monster known as Evil Natural Water hasn't had too much focus yet. It was known to be extremely powerful, and even the Monster Association wasn't able to communicate with it, opting instead to keep it locked away. Appearing as a liquid mass with floating eyeballs, Evil Natural Water was able to draw on the local groundwater once it escaped, growing larger as it transformed more water into itself. The hero Blackluster was fairing pretty well in his fight against it, but ultimately it survived his attacks and even withstood Garou's rapid barrage.
Now, the creature's liquid body has gotten close enough to the coast that it's begun assimilating the entire ocean, causing its eyes to grow larger than an aircraft carrier. Part of what makes Evil Natural Water so dangerous is that it responds to hostile intent and reciprocates immediately--that's why it attacked Garou and why it didn't attack King. That was definitely a problem when it was facing off with heroes, but now Evil Natural Water is coming in contact with civilians and military personnel, whose logical immediate response is terror and aggression. The more damage it does, the more people will fear it and feel the need to defend themselves, locking the world into a potential spiral of increasing devastation.
Evil Natural Water's destructive potential really can't be overstated, and attacks from dispersing it to freezing it have all failed to even slow it down. Since it seems to run on "regenerate from a single drop" logic, like Dragon Ball Z's Cell, it may well be impossible to defeat entirely. Worse still, being made of water makes it difficult to attack physically, which rules out the majority of heroes' attacks. While Saitama has yet to face off with the liquid beast, there's not much reason to think his punches would fair any better than Blackluster's or Garou's. The one advantage he does have has less to do with the physical force of his punch than the side effects: a strong enough attack could generate a shockwave, with increased pressure and heat causing Evil Natural Water to evaporate. There's no guarantee that would work, either, but only Saitama could even give this tactic a try.
While the heroes have been gaining the upper hand in recent chapters, having finally defeated Fuhrer Ugly and had Homeless Emperor taken out by his own God, that doesn't mean they're out of the woods. Platinum Sperm and Evil Natural Water may be the only remaining executives, but the battle for mankind's survival in One-Punch Man is far from over.