User blog comment:Freadliest warrior/Godzilla vs Gamera is HERE/@comment-24974663-20140818102439/@comment-1030114-20140820120909

In addition, Gamera's smaller weight means that had he succeeded in using the Fireball Ejection Suicide attack, he still would not be able to kill Godzilla because of the limited amount of energy his smaller and lighter body contains. He only killed the Gyaos using that move because they were smaller than him. Thus, Godzilla would be injured by such a move, but then his regeneration needs to be taken into account.