Japanese title: 冥王計画ゼオライマー (pronounced as Project Zeorymer)
Official English title: Hades Project Zeorymer
A manga and OVA series by Takaya Yoshiki (going under the pseudonym Chimi Morio), though the two versions have completely different settings and stories. The OVA version features mecha and character redesigns by Moriki Yasuhiro and Kikuchi Michitaka respectively.
The original manga was followed up with a sequel in Hades Project Zeorymer Omega.
Features one of the most overpowered main character mechs ever.