Universal Century 0079. At the start of the One Year War, while the Zeon forces deployed the "MS-06 Zaku" in actual combat, the Earth Federation Forces lacked any real MS combat power and fell far behind. To close this gap, the Earth Federation Forces initiated the MS development plan "Operation V." Based on the RTX-44, the "RX-75 Guntank" was developed. Using information from captured Zakus, the RXM-1 was developed, followed by the RX-77-1 Guncannon. The RX-77-1 evolved through test machines into the "RX-77-2 Guncannon," which led to the development of the "RX-78-2 Gundam." The technologies gained from Operation V were selectively refined and passed down to the RGM-79 GM.

While the Gundam was the machine that symbolized the One Year War, the Guncannon was also an outstanding MS. A high-firepower, high-defense machine primarily armed with 240mm low-recoil cannons for bombardment, also capable of using beam rifles and close-quarters combat. Its mobility and maneuverability surpassed the Zaku, and some models were even able to hold their own against the Gelgoog.

Six RX-77-2 Guncannons were initially produced. Three were deployed to Side 7. Two were lost to Zeon attacks, but the remaining one was brought aboard the White Base, designated "108," and piloted by Kai Shiden. Of the remaining three, one was deployed to the Federation front lines, one was deployed to the 8th Transport Unit based at Luna Two and designated "801." The final one was later sent as a reinforcement to the White Base, designated "109," and would be piloted by Hayato Kobayashi.

[Story] you was involved in the design of the Guncannon's appearance. The completed Guncannon and you were being transported by the 8th Transport Unit's transport ship, the Noahfreighter, when they were attacked by Zeon forces mid-transit. you, knowing the Guncannon's systems, was forced to pilot it and experience actual combat. Following this battle, the utility of operating an MS from the transport ship Noahfreighter was recognized, and the Guncannon and you were officially assigned to the 8th Transport Unit, receiving the unit number "801." Thus, you and the Guncannon 801, as part of the 8th Transport Unit, set out on transport missions alongside the Noahfreighter. This is the story of the pilot of one Guncannon who fought in the shadows of the One Year War's history.