From MangaHelpers:

A man who goes by the code-name Procyon and his allies, including Spica and Sirius, are being dispatched to protect Earth from alien invaders. Procyon's real name is Nagare Seishiro, and, once on Earth, he meets a woman that he can call nothing less than a goddess. They promptly get married, to the dismay of her 9-year-old son, Ikuru. Ikuru is even more horrified when his mother is transferred overseas, leaving him to live with his new weirdo "father." Nagare comes and goes at random hours, but won't tell Ikuru what he does at work (fighting aliens as the Earth's protector, Procyon). Nagare also doesn't seem to quite grasp some Earth customs. For instance, he makes his meals by taking all the separate foods and then blending them into a liquid. Ikuru refuses to accept him as a father, but he loves watching the exploits of the awesome Procyon. Will Nagare be able to get through to his new son without betraying his secret identity, and keep up with his work protecting Ikuru and the other humans? [tethysdust]