A Romance of the Three Kingdoms retelling using SD Gundams.

The land of Neotopia is attacked by the Dark Axis, evil invaders from another dimension who wish to conquer this land. Neotopia's answer: the secret Super Dimensional Guard and their defenders, the Gundam Force. Led by Captain Gundam, the Gundam Force and its team of Gundams with special abilities are aided by a boy named Shute as they stop at nothing to defend the land from the Dark Axis and to defeat them once and for all. (Source: ANN)

In the distant future, humanity has explored beyond Earth and colonized both the inner and outer planets of the Solar System. In order to protect the colonies and maintain law and order in the solar system, the Earth Federation Government (EFG) was created. Soon, many settlers started to resent the EFG's and its sphere of influence, straining the relationship between the central government and the colonies. While a strained peace was being forged between Earth and the colonies, a race of non-human creatures known as Deathcula invaded the System. Without provocation, they attacked the colonies and killed many of the colonists. The EFG quickly realized that the Deathcula were technologically superior and their forces were hopelessly matched. In order to have a chance at survival, Dr. Charles Louvre developed a transformable starship known as the Bismarck. Knowing that an advanced team of specialists were required to operate the Bismarck, four individuals came together and were charged with keeping the outer colonies safe from further Deathcula attacks. (Source: Wikipedia)

In 1990, Bandai produced the 4 episode OVA series SD Gundam Gaiden. Directed by Tetsuro Amino (Macross 7, SD Gundam's Counterattack), this series is set in the medieval fantasy world Suda Doaka. Once again, popular Gundam characters such as Amuro Ray and Char Aznable are featured in the series, along with fantasy-styled versions of well-known mobile suits. In this series, the heroic Knight Gundam and his companions must protect Suda Doaka from the evils of Satan Gundam and Sieg Zeon. Much of the series is set in the Kingdom of Lacroa, which is featured in several SD productions, including the 2003 TV series SD Gundam Force. As is the case with all the older SD productions, SD Gundam Gaiden isn't available in the U.S. (Source: AniDB)