Marina was a 2 for 1 Combo Monster(s) of the week in Ep.22 of the Kotetsu Jeeg Anime. It was compose of two components: a Red and Brown Humanoid Rider Phantom with an Yellow two blade fin on the head, that was located on the top of the Shark's forehead, & the Shark itself, which was Lavender in color, with an armor plate on top. They could separate (the Humanoid actually having legs) to cover more ground to destroy its enemies, with the Shark doing most of brute force, while the Humanoid use its trident & fire breath. The shark would have a Red Horn in the spot where the companion sits while ejected.

After remembering the many failed attempts to defeat Jeeg lead to the destruction of her Phantoms thus far, Himika's hopes to defeat the robot lies with a Dragon she found in the other world, but can't open the door without the Bell and orders her Ministers to find ways to get the it.

Time later, a Ferry leaves dock; on board is Mayumi is in Class Field excursion, among them her close friend Tomo and her Pet Dog, Koro (from Ep.20). Koro sneaks away and the girls follow him into a Cargo Hull where he growls at a trunk. The girls open it to find a bomb but before they could go warn anyone, they are stopped by Mimashi and a room full of Jamatai Warriors, the girls and Koro are knocked out, and the villains seize the ship, taking its passengers and crew hostages, killing or wounding some in the take over. Soon after, the news spreads through bulletins and Hiroshi heads to the dock where the Orochi appears where one of the Ministers demands the delivery of the Bell or the people on board will be kill; he calls them cowards as the Orochi disappears, and vows to save the hostages with his own strength.

Back at the Ferry, an entire fleet or coast guards surrounds the vessel, but is unable to come close as the Jamatai had installed Deck Guns while many others surround the hostages with their weapons. As Hiroshi arrives on a speed boat, as well the Big Shooter, the Phantom (Marina) emerges destroying the fleet; Mimashi calls Hiroshi out and gives him once more the ultimatum to deliver the Bell. Hiroshi retreats and returns to the lab to demand answers from his father though he is unable to say despite the life of Mayumi and the others been at risk, Michi and Dairi had to hold Hiroshi from attacking the Computer Father, Michi reminding him the sacrifice he did when protecting the world when keeping the secret. With time running out, Hiroshi and Michi take the Shooter to return to the ship, on the way, Hiroshi formulates a plan.

The Shooter arrives to the Ferry; expecting the Bell, Mimashi sees Hiroshi parachuting and is shutdown, his body falls on deck and its stab by the warriors, only to find its a Dummy. The real Hiroshi appears having sneak onto the vessel via scuba diving, and shots a few guards with a harpoon gun. He then takes a stand against the Jamatai, while avoiding the Deck Guns, with the Big Shooter providing cover by blowing the villains away with flybys. Mimashi and the Warriors retreat with the help of Marina, while Hiroshi releases and warns the captain about the bomb; He and crew releases the passengers, and try to abandon ship while Hiroshi searches for the bomb, only for Marina to return, trying to stop the passengers from leaving the ship. Michi warns Hiroshi who then comes out and transforms to combat Marina using the Mach Drills to dive after the Phantom, while Michi searches for the Bomb.

Side Note: Due note, Hiroshi's sudden arrival causes a small plot hole. Back in Ep.11 he was knocked out by the Haniwa Phantom Garuga https://www.furaffinity.net/view/34526410/ , and he sank to the bottom of the lake and spent an hour unconcious before coming out. We know he doesn't need to breath Under Water so why the air tank?

In their underwater fight, Marina avoids Jeeg's Spin Storm, then smacks the robot with a tail whip; The Humanoid Rider ejects while the Shark holds Jeeg, allowing the former to cover it with the Fire Breath (yes, fire Under Water!!!). The Shark rams Jeeg on to the rocks, the Humanoid dashes for a kill, but is stop by MechaDon2; the Rider cuts the Robot's arms, forcing Don and Pancho to abandon it, but are corner by the Shark and the Rider; Jeeg dashes at full speed into the Mouth of the Shark, destroying it, saving the two pilots and leaving the Rider to deal with.

On the ship, Koro sneaks his way out of the Hold to finds Michi and guides her to the girls and the Bomb; she grabs the Bomb and throws it into the sea where it explodes, saving the Ferry and those that remained. Meanwhile, the Rider attempts to escapes by going deeper, but its body begins to crack by the pressure; Jeeg uses Magnetic ropes to hold it but Marina throws its spear to break free; Jeeg then fires Spin Storm, destroying the Phantom.

After the battle, the Ferry returns safely, with Tomo thanking Koro for saving them, while elsewhere, Hiroshi is left wondering of the Bell's location and if it has to do anything with the secret of his body.