Distributor Shout Factory is doing a little streaming that kind of flew under the radar with the addition at some point of the three Danguard Ace compilation films. The work came out back in 1978 based on the original creation by Leiji Matsumoto. Animated by Toei Animation, it was directed by Masayuki Akehi abased on the screenplay by Tatsuo Tamura. The features are in their English language adaptation only owing to it being of interest to old school fans that grew up with this property.
Plot concept: Evil scientist Doppler will stop at nothing to destroy the giant transforming robot Danguard Ace, so he can conquer a new planet.