There exists a place called Eden where angels live and watch over the humans who they call Earthians. Because the Earthians are not being good beings the angels have decided to take action. Pairs of investigating angels are sent to the Earth to monitor the Earthians. One is a plus checker, the other is a minus checker. If enough minus checks accumulate then the Earthians will be annihilated. The story Earthian centers around a pair of investigators named Kagetsuya and Chihaya. Kagetsuya is a minus checker and Chihaya is a plus checker. Chihaya is the main protagonist of the story. Chihaya is unusual because he was born with black hair and wings but everyone on Eden has blonde hair and white wings. Earthian is usually about Chihaya's relationships with Earthians, angels, other forms of life and especially Kagetsuya. And what is the mystery behind Chihaya's black wings? Is it just a genetic mutation or is there some other deep reason he was born this way? Things get even more complicated when Chihaya and Kagetsuya fall in love... On Eden, homosexual love is forbidden.