Getter Robo Hien: THE EARTH SUICIDE

This series continues the Ken Ishikawa continuity of Getter manga, temporally taking place after Getter Robo Go and before Getter Āḥ. The series features an older Hayato leading a new team of Getter Pilots (and a new Getter) as they defend the earth from large plant-like monsters.

(Source: Wikipedia)

Note: Includes an extra chapter that was published on the last volume.