Wikipedia, quotes.
↓ Getter Robo Armageddon, known in Japan as Change Getter Robo!!: The Last Day of the World(真ゲッターロボ!! 世界最後の日Chenji Gettā Robo!! Sekai Saigo no Hi?, anime title) and True Getter Robo(真ゲッターロボShin Gettā Robo?, manga title), is a manga and original video animation released in 1998 by Bandai Visual, based on the manga and anime series Getter Robo, created by Ken Ishikawa and Go Nagai. The series, however, owes more to the manga than the 1970s animated adaptation, with designs closer to those of Ishikawa's original art, and a darker, more serious tone than the anime. It is a direct sequel to the audio drama 'Getter Robo: The Moon Wars'. Aside from the main characters and titular mecha, Getter Robo Armageddon and The Moon Wars have no relation whatsoever to previous Getter Robo stories, instead taking place in their own continuity.
