The Fandom Post is reporting that Amazon Prime is now streaming the Mazinkaiser SKL anime OVA on its service. The OVA is available with the original Japanese audio and English subtitles.
The story of Mazinkaiser SKL is described as:
Above Japan waits Remuria, a colossal floating island leftover from the last world war. It’s a lawless wasteland of robot super-weapons from a forgotten age of military might. Receiving word that the unstable island’s reactors might explode and vaporize Japan at any time, the Japanese government awakens the most destructive force ever devised: MazinKaiser.
Source: The Fandom Post