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.

[Source: Anime News Network; emended]

After successfully returning to Earth on the renovated Stratos 4, the four main characters are visited by the Comet Blasters Chizuru Kubo and Annette Kerry, who bring them a shocking video. Meanwhile, Orbital Station 7 is in serious trouble...

This two-episode OVA comes between the first and second seasons.

[Source: Anime News Network; emended]

This short episode comes along with the first episode of the OVA.

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.

Stratos 4 Recap episode - For everything which happened before Stratos 4 Advance started.

Crisis befalls the main characters and the Earth as well! How do they deal with the conspiracies that they have uncovered, while protecting the Earth too? (And what happens to the cliffhanger at the end of the previous episode?)

In these final two episodes of Stratos 4 Advance are the exciting conclusion to the whole Stratos 4 series. The main characters will have to draw on all the resources they have, their friends and allies and their own sheer force of will, to "bring tomorrow to Earth," as one of the characters puts it.