Ultraman Cosmos 2: THE BLUE PLANET is a direct sequel to the original Ultraman Cosmos television series. In the movie it has been a year Musashi retired from being a Team EYES member and now he has finally pursuiting his dream to become an astronaut. Musashi pilots his Planet 1 aka. TECCH Spinnar KS-1 and went on a journey to Planet Juran. However, much to his horror, the planet appeared to be a reddish and dusty wasteland. Not only that, Parastan, the Planet’s protector died. Suddenly, a flying monster burst out from the ground and firing a reddish energy ball. As it about to ram Musashi’s TECCH Spinnar KS-1, Ultraman Cosmos appeared and save him. As they dueled, Musashi founded that the monster is responsible for turning the Planet Juran into a barren wasteland via its energy beam. Cosmos destroyed the monster, causing a giant explosion and quickly rescuing Musashi from the explosion.
Musashi attended his childhood friend’s wedding in Saipan. His friend Mari caught the bouquet. During her lunge, Musashi saw a strange woman in the ocean, who suddenly leapt into the air, proving to be a mermaid. One of his friends, Tutomo, mocking him for believing he saw a mermaid but Mari objects, implied that Musashi might be talking the truth ever since his first encounter with Cosmos. As it starts to rain, Tutomo cowardly hides under the table with Mari mocking him, causing Tutomo to take a nearby soda and spraying it on Mari, starting a soda fight with his friend as they watched again by the mermaid.
The next day, when Musashi and Mari went snorkelling, they discover a portal underwater and at the same time ambushed by a stingray kaiju. As Musashi about to follow Mari, he knocked down unconciouss. Later, to figures approach to him. One a man and the other a woman/mermaid that he witnessed before. The man decide to eliminate Musashi for interfering them but the objects, only for too late as he already fire an energy blast to Musashi. He awakens at the hospital as his friends visits him but Mari was nowhere to be seen. Then, Koji, an original member of SRC and now a captain of Team SEA approaches him as he glad that he survives. Musashi was taken to their base and revealed that the monster he encounter earlier was Reija, who was detected undersea a year ago.
They were interrupted by a warning where a monster named Scorpiss entering the Earth atmosphere. Musashi recognise him earlier for turning Juran into a barren wasteland and killing Parastan. Musashi joined by Team SEA launches with their TROY AS and TROY BS. As the monster rampaging at the city, it begin to destroy a hospital that Musashi’s friend reside. Once they about to be killed, Team SEA fires a missile, bringing it away from the hospital. Reija appears and fought the monster but only to be overpowered by the menace. Musashi exits the TROY BS and bring his friend to safety.
There, he witness the mermaid, now having a human legs fuses with Reija, turning the monster stronger but still, overpowered by Scorpiss. Musashi takes his Cosmos Stone and transform into Ultraman Cosmos Phantom Corona Mode. The phantom-looking Ultra rescues Reija and overpowers Scorpiss while destroying it with Phantom Blazing Waze. However, all he foreseen was a dream and realise that Cosmos will never return. Scorpiss retreated for a while and the mermaid reveals her name as Shau while telling Musashi that Mari is with her people.
Soon the Team SEA is led by Shau and Reija under the sea to where a portal opens, leading to her people’s hideout. Once arrived, they were introduced to Alien Gyashi, where their leader, Jin, holds a dislike towards humans for being selfish. Musashi encountered him earlier in a dream where he got destroyed by Jin. Mari appears and leads them to their base where she revealed that Child Baltan from 10 years ago that brought her to this place.
Shau reveals that sometime ago, Sandros and his Scorpiss terrorize their planet and turn it into a wasteland. As the Alien Gyashi migrated, Scorpiss chase them and destroy them. When Jin’s crew about to be eliminated, a being with light silhoute destroys them and let the remaining Gyashi flew safely. The being itself had been acknowledged as a God by their species.
A swarm of Scorpiss arose and on their journey to Earth in 7 days. Team SEA discuss this matter with Earth Defense Forces where they agreed to have the Alien Gyashi assist them in protecting Earth from Scorpiss. 3 days before the Scorpiss invasion, SRC developed a force field used to defend the Earth from the monsters. Musashi receives a call from Mari to go to Space Zone. There he found Mari unconcious and Jin begins to attack Musashi for making Shau trusting humanity. However, he stops when realises that Musashi didn’t fight back and instead offered his hand in peace, never giving up on convincing him to trust humanity.
Developing a change of heart, Jin uses his power to complete the force field system, causing a giant shield to cover the Earth and protecting it from a swarm of Scorpiss. Though proven effective, but a dark vortex empowered some Scorpiss as they were used to perform a kamikaze attack to destroy the shield and ease the invasion. Soon, Team EYES started to help as Musashi, their former team member also involved in this operation.
After witnessing Shau and Jin’s bravery, Musashi finally regains his bravery and call Cosmos once again. Cosmos appears in Eclipse Mode where he demolishes the entire Scorpiss before Sandros appeared and overpower him. Another Ultraman much like Cosmos, whose the legendary God/protector of Alien Gyashi came to Earth at the end of the Scorpiss invasion. Attacking the invasion’s forerunner, Sandros, at the moment it attacked Cosmos. The Ultra knocked the monster to the side. As it recovered, he delivered some of his energy to the weakened warrior, allowing them both to take on the vile monster.
As they did so, Sandros began to unleash its black cloud, blocking out the sun. In complete darkness the pair of heroes was attacked mercilessly by its energized blades. The foolish monster, however, eventually made a mistake. Charging up its fire ball exposed itself in the darkness, allowing both Cosmos and Justice to quickly fire off their Cosmium and Victorium Rays, annihilating the fiend and saving the Earth yet again. Cosmos separated from Musashi again as the Ultras leave and Jin revealed to be survived from the Scorpiss attack thanks to Reija and that their experiment finally reaching its success.
Sometime later, Cosmos repairs the damage done by Scorpiss as he and the Alien Gyashi spaceship fly towards the sunset, ending the movie.