After being kidnapped by a mysterious organization, Masato's life is changed forever when he discovers that he was born to pilot the robot "Zeorymer of the Heavens". But exactly what is Zeorymer, and what is the nature of Masato's birth? Masato searches for the truth as a group known as Hau Dragon search for this robot and attempt to destroy the only thing that can stop them from world domination. Every battle brings Masato closer to the truth -- a truth that he may not like once it is revealed.
Tomoru Shindo yearns to become a pilot and taste adventure, but the rigid structure of his advanced society leaves him bored and wishing he was born into the chaos and romance of the past. This simple wish turns into reality when a chance encounter with a Dr Kanzaki gets him involved with the greatest conflict that will engulf Earth yet: the invasion of Earth by the alien race, the Evoluders. Dr Kanzaki was building an Evoluder whose data had reached Earth, and Tomoru finds that he can link to it and access its memories. Its name is Orgun, and seems to have a connection to Tomoru, and Tomoru's past...
If your like me, you really like that 90's mecha feel. it was before the CG had come in and the machines moved and flashed by the screen with detail that you know someone sweated hours and hours over.
It also helps that both are OAV's so the money was not as much an object as if it was a TV series.
So if your looking for another short Mecha series and you have already seen one, try the other. The stories are not really that close in relation, but mecha is mecha, especially in the 90's