Gekigangar III is a "meta-anime" of the anime series Martian Successor Nadesico that plays a critical part in the plot thereof. Initially, only Gai Daigoji and Akito Tenkawa are depicted as enjoying the series. After Gai's death, then Hikaru becomes the other resident anime fanatic.
The story is as follows. Ken, Joe, and Akira, 3 ordinary high school students, are also the pilots of the super battle robot Gekiganger 3 (itself made up of 3 smaller robots). With the help of the Kokubunji family, they team up to fight the evil Prince Akara and Emperor Hyperion of the Dark String Universe, who wish to take over Earth.A.
The title, Gekigangar is a parody name with Gekiga and "-er" combined meaning "people of/from serious manga". The look and plot style of the Gekigangar clips are derived from older Super Robot anime shows, like Getter Robo and Mazinger Z. (Wikipedia)