The series follows high-school student Daichi Manatsu who starts working for the Globe organization to pilot a giant robot called the Earth Engine Impacter to protect the Earth from the invading alien force known as the "Kill-T-Gang", that intends to drain all the life force of mankind to empower their immortal existences.

High-school student Daichi Manatsu works for the Globe (グローブ, Gurōbu) organization to pilot a giant robot called the Earth Engine Impacter (アースエンジンインパクター, Āsu Enjin Inpakutā) to protect the Earth from the invading alien force known as the "Kill-T-Gang" (キルトガング, Kirutogangu), that intends to drain all the life force of mankind to empower their immortal existences.

In order to aid Daichi, Globe starts gathering allies including Teppei Arashi, a Kill-T-Gang whose memories have been erased and trapped inside a human's body; Hana Mutou, a mysterious girl connected to the ship Blume; and Akari Yomatsuri, a 17-year-old genius hacker.

Kill-T-Gang have access to special abilities known as "singularities" that differ on the individual but have the common trait of both sharing memories and communicating telepathically through kissing.

Because the Kill-T-Gang's true forms absorb libido through proximity, humanity would be wiped out should even one make it to the Earth, necessitating the use of Impacters.

Unlike his previous work, Star Driver, Captain Earth focused less on high schools and more on the relationship between human characters who pilot mechas.

Something the team was aiming for with Captain Earth is having a good looking launch sequence as he believes "robots and rockets are deeply imbued with childhood dreams and that sort of giddy excitement in boys’ hearts.

[44] Andy Hanley from UK Anime Network called it "Eureka Seven meets Star Driver", and noted that this might grab the attention of fans of the prior works.