Katori and Haruka do some shopping for groceries. Haruka wonders why Hiroshi asked for black ink when he’s working on his own Miracle Ink invention. Back at the Amano Peace Labs, Hiroshi tests out his Miracle Ink which can write anywhere by using it on the window glass. The ink however catches fire and Hiroshi burns his hand. He reflexively jabs his hand into a nearby fish tank while Kenta puts out the fire. Kenta then notices that Hiroshi accidentally spilled some of the ink into the tank, but it quickly vanishes without any ill effects to the fish. Over lunch, everyone discusses the incident and Hiroshi reveals that not only did the ink purify the water, but it also generated oxygen and minerals. Kenta suggests they rename the invention and Hiroshi changes it to Miracle Water Cleaner. Haruka serves grilled sardines but Kenta refuses to eat them. Katori suggests that Kenta eat the tropical fish but everyone tells him that those are only for ornamental use. Elsewhere, Jango proposes his new plan to destroy all the world’s seawater, which involves spreading a manmade toxic red tide all around the world. On the coast of Okinawa, Momoko reports the grand opening of a sea farm used to breed fish. In the underwater promenade area, Ippei and Goro are cleaning the glass when they spot a mechanical monster out in the water. Momoko receives word of the red tide and quickly announces it from the news chopper. Katori asks what red tide is and Hiroshi explains that it’s an abnormal growth of plankton that uses up all the oxygen in the water. Aqua Baron collects a sample of the water and brings it to Hiroshi, who reports that it’s spreading at a phenomenal rate and will destroy all the world’s oceans within a month. Kenta quickly suggests using the Miracle Water Cleaner, and Hiroshi sets out to make large quantities of it. The Japanese coast guard deploys booms to slow the red tide’s advance but the mechanical monster emerges from the water to complicate things. Hiroshi quickly dispatches Katori and Kenta in the Fire Jet to buy him time to produce the Miracle Water Cleaner.
The monster destroys the booms and spreads the red tide further, knocking over the coast guard boats. It’s about to attack the crew when Katori arrives and knocks it back with missiles. Katori drops lifeboats for the crew and Momoko orders the helicopter pilot to get closer for a camera shot. The monster knocks out the helicopter’s rotors and Katori grabs it with a magnetic grapple line before it falls into the ocean. He sets it safely on solid ground then combines with the Fire Jet into Fighbird. Fighbird attacks the monster, piloted by Zol, while Momoko chases after Kenta to ask him questions. Zol grabs Fighbird with the monster’s pincers and blasts him with corrosive liquid. Kenta cries out for him and allows Momoko to discover Fighbird’s name. She tries to ask Kenta where Fighbird lives but he runs away from her. The Baron team arrives and blasts Fighbird free. They then fire missiles containing Miracle Water Cleaner into the ocean. Momoko corners Kenta but they both notice the red tide disappearing, with Kenta noting that the Miracle Water Cleaner worked. Zol tries to run away but the Baron team combines into Thunder Baron and chases after him. He grabs the monster with his Thunder Anchors and flings it back to the surface, allowing Fighbird to destroy it with his Flame Sword. Momoko goes back to pestering Kenta for answers but he evades her and falls into a pool of fish in the process. She thinks she has him trapped but Katori picks him up in the Fire Jet and flies away. Momoko swears she’ll discover Fighbird’s identity. Back home, Hiroshi tells Kenta that he could’ve gotten away from Momoko if he was taller, hence he must eat his sardines to get more calcium. Haruka offers the sardines fried and Kenta still refuses to eat them, but when Katori shoves one in his mouth he actually finds it delicious. He asks for more but Hiroshi protests that there won’t be any left for himself.
Another run of the mill episode peppered with a few quirks. Jango once again channels a Captain Planet villain and goes after humanity from an environmental angle. Ippei and Goro pop up trying to make an honest living, while Momoko tries to pry some answers out of Kenta but only manages to get Fighbird’s name. On the other hand, while the series so far had a bit of an educational bent, this episode lays it on pretty thick with Haruka correcting Katori’s pronunciation and Hiroshi espousing the virtues of eating fish to Kenta. It was also a little too convenient that Hiroshi just happened to accidentally create a very potent water purifier when he was trying to make a universal substance adhering ink.