Chouju Sentai Liveman (1988)

Academia was a school for scientists located in Academia Island. One day, Academia's Top Three students (Tsukikage, Senda, Omura) were kidnapped by Bias. In the process, Tsukikage kills Yano Takuji and Aikawa Mari. Two years later, Volt destroys Academia. Three surviving students (Yuusuke, Jou, Megumi) Find out that the three kidnapped students lived-as Kempu, Mazenda, and Obular. The trio become Liveman to fight their former friends. Later on, Takuji and Mari's younger siblings (Tetsuya and Jun'ichi) join Liveman.