Musashi Haruno, a member of the science investigation team EYES with dreams of peace between humans and monsters, has to deal with the Chaos Header virus, which is corrupting Earth's monster population into violent berserkers. Soon enough, he meets again with his childhood friend Ultraman Cosmos, and together they strive to heal the monsters' blight.
The series has its own feature film prequel, Ultraman Cosmos: The First Contact, which depicts Musashi's first contact with Cosmos.
Cosmos takes a much Lighter and Softer approach to the formula, with a kinder and gentler Ultraman that mostly fights on defense and prefers to save monsters instead of killing them. While the series is a major opinion-splitter among Ultra fans, the movies are generally well-liked.
Ultraman Cosmos provides examples of the following tropes:
- Alternate Universe: From the Showa-verse, Tiga/Dyna-verse, and Gaia-verse.
- Anti-Villain: Believe it or not, the Baltan in the first movie.
- Big Bad: Chaos
- Gondor Calls for Aid: The bonus of living in a universe where many Kaiju and aliens are decent beings is that they would occasionally come to Cosmos's rescue if needed.
- Eldritch Abomination: Chaos Header.
- HeelFace Turn:
- Many of the monsters do this, due to Cosmos preferring to pacify or purify them instead of killing them.
- Chaos Header ultimately does so in the end, transforming into an angelic being and leaving the planet willingly upon being purified and having a Heel Realization. We find out in a follow up that it becomes the guardian of a planet acting as the sanctuary for benevolent or benign monsters.
- Lighter and Softer: One of the lightest entries in the franchise.
- Lovecraft Lite: Chaos Header.
- Multiform Balance: Interestingly, at first this is less 'this form is strong and this one isn't' and more 'combat mode and pacify mode.' Luna form has no Finishing Move and largely is devoted to pacifying and purifying it's opponents while Corona mode is more combat based and actually capable of using lethal force. Eclipse Mode is a combination of both and has the ability to do either, and it's Finishing Move can purify good monsters and destroy evil ones (sometimes at the same time).
- Rousseau Was Right: Many of the Kaiju and aliens, if not the humans, are decent beings in essence. This includes Chaos Header.
- Space Whale: The Fake Space Whale Jirak, who is gentle as can be. Then Chaos Header does what it usually does.
- Technical Pacifist: Cosmos, to the point where his default Luna Mode has no finishing attacks at all. He will only switch to his more powerful Corona Mode when there is absolutely no other option or when he's facing something that's completely evil.
- The Virus: Chaos Header.
- Turns Red: Cosmos changes color from blue and silver to red and silver with blue patches when transforming into his Corona Mode. This is justified further by the fact that Cosmos usually changes into Corona Mode once he has suffered at least some injury.