The episode title spoils the twist?
So, this is a solid action episode, featuring our trio (as of adding Aira) against the Serpoians and their hired goons: Mantis Shrimp Alien and Laser Nessie (also implicitly an alien). This mostly starts out with just Okarun and Aira fighting back against team alien. Aira’s powers take them by surprise at first, but they manage to rally fairly well even as Okarun abandons the quest for clothing in order to re-enter battle. Just when it seems like they’ve won, the cavalry arrives in the form of Momo. It’s not made totally clear how she got away from Nessie, but she can cancel out the Serpoian psychic powers with her own, making it a fairer fight.
The Serpoians empower their gig worker to take on an even shrimpier form with stronger punches, but as long as Momo can keep focus (not always the easiest under the circumstances) Okarun and Aira can fight back.
The aura color changes, though, as Nessie arrives. The beast turns on the Serpoians, or just generally whatever is in the area, and also turns all the solid objects to fields of water. Underwater, Mantis Shrimp can punch even more powerfully, which forces Momo to get creative with how to get everybody moving.
After getting through the physics glitch that is this battlefield, our three heroes get a chance to strategize… and the Serpoian that remains gets a chance to instigate a fusion with both Nessie and the gig worker, resulting in the titular Serpo Dover Demon Nessie (even though if the show introduced the mantis shrimp gig worker by his Dover Demon alias, it was a blink-and-you’ll-miss-it moment I missed) It has all the intellect of the Serpoian master, Nessie’s water laser at grand scale, and is revealed to have mantis shrimp punches as well, making the effort to get in close and disable its neck difficult.
However, it turns out Mantis shrimp can’t go all-out in air, something that the Serpoian didn’t realize, at least not fast enough to stop Momo from creating a nice bubble just as it tried to punch her. With its arms disabled, Momo keeps its attention while Aira creates a path for Okarun to go all out and hit the thing into next week.
Thus, this is the state in which our characters exit the field: Okarun (naked) atop Momo (down to her underwear), having overcome their friction and happy to be alive, laughing in joy at having the solid ground of a school hallway once again.
Wait, school hallway? Cue the animation going full deranged to sell their panicked, streaking flight as the episode plays us out.
Thus ends this particular little arc. We’ve got three episodes to go in the season, and I’m looking forward to seeing what they get in this time.