Zillion

The story takes place on the planet Maris in the year 2387. Around this time, the Nozas started to genocidally kill all humans in order to lay eggs and reproduce on the planet. Three mysterious guns dubbed the "Zillion Weapon System" appear and three teens (JJ, Champ, and Apple) are chosen to wield them as the White Knights in order to fight back against the Nozas.

(Source: Wikipedia)