在这部假面骑士天空骑士 8大骑士vs银河王动作/冒险/剧情片中,罗门博士在宇宙开发出了新的氢能，但在往返地球的途中却遭到银河大帝所乘飞碟的袭击。博士让爱犬带着氢能方程式回到地球，但爱犬却在回到地球后被新修卡的怪人抓获。得知此事的洋变身为天空骑士与新修卡的怪人展开战斗，誓要夺回方程式，而此次众多假面骑士前辈亦出手相助……
The movie begins in space, on a space station. A space team called, TENKA, was testing a super-powered weapon on a deserted planet. It worked, so they celebrated. But Galaxy King saw this, and decides to attack the space station.
