Loveless is a Japanese manga series written and illustrated by Yun Kōga. Kōga plans to end the manga at fifteen volumes.
In his first day at his new school, a then twelve-year-old Ritsuka Aoyagi meets a mysterious twenty-year-old male named Soubi Agatsuma. Soubi claims to be a good friend of Ritsuka's brother, Seimei, who was murdered 2 years earlier. Upon the inspection of Seimei's abandoned computer files, Ritsuka discovers that an organization called 'Septimal Moon' was responsible for Seimei's death. As Ritsuka quickly discovers, Seimei and Soubi acted as a pair involved in spell battles invoked by carefully selected words. Now Soubi is Ritsuka's 'sentouki', or Fighter Unit, and Ritsuka is his 'Sacrifice'. Together, they challenge Septimal Moon to find out the truth behind Seimei's murder and the reason for Ritsuka's amnesia, and form an intimate bond as they unravel the mystery.
The most immediately noticeable aspect of the story is that many characters are kemonomimi—cat-like features (in this case, ears and tails) are universal from birth, so there are as many catboys, including the protagonist, as there are catgirls. People in the Loveless universe lose their animal features when they lose their virginity. Those who no longer have animal features are differentiated by society as "adults".