Takeshi, is an orphan teenager living in blue sky orphanage. On his 16th birthday, a strange old man named Ruby comes to pick him up, claiming he's the subordinate of his father, who was the ruler of Apolon planet.
Takeshi's father invented a machine named Hearth Energy which produces unbelievable power. However, Apolon was attacked by Armies of Dazan planet and they stole the Energy Heart and killed the king.
However, they can't use Energy Heart, because its key is hidden in Takeshi's chest, the only heir of the lost kingdom.
But Takeshi has been located by Dazaan and they'll soon come to get by any force, even by destroying Japan. Ruby asks Takeshi and his friends to use Apolon's UFO technology to defend Japan, take back the Energy Heart from Dazaan Army and avenge takeshi's father.

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Sequel: UFO Senshi Dai Apolon II