At a time when Earth is about to be threatened by sinister aliens and monsters, Agent 340 from Nebula M-78 (the same planet Ultraman came from), who was originally sent to make a map of the Milky Way, decides to stay on Earth, and seeks to protect it.
Disguised as a mysterious human named Dan Moroboshi, he is invited by the Terrestrial Defense Force to join its elite branch, the Ultra Garrison, as its sixth member to combat the threats from space. Little do the other 5 members of the Garrison know that whenever the situation becomes hopeless, Dan secretly puts on the Ultra Eye glasses, and becomes his true form of Agent 340, christened by the Garrison as its honorary 7th member, Ultra Seven!
Seven would later return in Ultraman Leo where after having his leg broken while trying to stop Magma Seijin and Giras, being saved in the nick of time by Leo, he becomes the captain of MAC. Even though he's reliant on a cane and unable to transform to Ultraseven, his Ultra Eye having melted after the Magma attack, he's able to help Leo out from time to time. Namely with his Ultra Willpower abilities that are able to temporarily incapacitate a monster and by using an updated Capsule Monster, Sevengar.