Koujirou moves to Tokyo from Japan's northernmost island of Hokkaido and insists on bringing his favorite horse, Hikarikin, with him. The alien king Rel arrives from planet Wedelun and gives him a belt that will allow him to transform into a Miracle Hero and to protect the world from alien menaces. He is more interested, however, in impressing the pretty Yuka, though his rival, Michinari, wants her for himself.

In this three-episode OVA, Taro learns more about Cynthia`s life as herself and her alter-ego Grace. He also undergoes training with his bodyguard Konoe. And finally, Ikuyo dupes Taro in spending a whole day disguised as a maid.

The Earth has developed a defense system against large meteorites that are on a collision course with it. This protection system is made up of the Comet Blasters based in several space stations as the 1st line of defense, using nuclear warheads launched by spaceships. The 2nd line of defense consists of the Meteor Sweepers launching from ground airbases using hypersonic planes with special missiles to deal with the resulting debris from the blasts. Mikaze is a troubled girl that is a trainee pilot for a Meteor Sweeper team that dreams of becoming a prestigious Comet Blaster pilot. Stratos 4 revolves around Mikaze's and her teammates' challenges to become real pilots, while the Earth faces the threats that come from space.

Having failed the Comet Blaster exams mysteriously, Mikaze and her friends are sent back to the Shimoji Island base, where, with three new Meteor Sweeper trainees around, they have been promoted to instructor positions. Meanwhile, more comets are on their way to Earth, and the mysteries behind the rift in the Cosmic Emergency Management Agency—as well as the alien parasites—begins to unravel.