Getter Robo
The "Getter Robo Saga" manga compilation by Ken Ishikawa ("Getter Robo", "Getter Robo G", "Getter Robo Go", "Shin Getter Robo", "Getter Robo Arc") is considered to be the main continuity of the franchise as each entry is connected to each other. The manga not by Ken Ishikawa, like Go Nagai's "Devilman vs Getter Robo" and "Getter Robo Darkness", aren't considered in the Ken Ishikawa continuity.