Space Pirate Captain Harlock

The Pyramid on the Sea Floor (1x7)

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Upon seeing an odd looking formation from space, Harlock's crew heads to the Bermuda area. Upon investigating a pyramid built by the Mazone on the ocean floor, they learn that the Mazone are actually a form of plant life. Learning that the Mazone are hidden across the globe and that the government has not heeded their warnings, the crew sets off on a search and destroy mission.