Loveless is a shônen-ai fantasy manga by Yun Kouga.On his first day at his new school, 12-year old Aoyagi Ritsuka meets a mysterious 20-year old man named Agatsuma Sôubi. He claims to be a good friend of Ritsuka's brother, Seimei, who was recently murdered, and the suspicious organization called 'Septimal Moon'may be responsible for the death. As Ritsuka quickly finds out, Seimei and Sôubi acted as a pair involved in spell battles.Now Soubi is Ritsuka's fighter, and Ritsuka is his 'sacrifice'. Together, they challenge the organization to find out the truth behind Seimei's death and the reason for Ritsuka's amnesia.
In the world of Loveless, everybody is born with neko (cat) ears and tails, which are shed after they have engaged in some form of sexual intercourse, thereby making the ears and tail a metaphor for virginity. This becomes a telltale sign about the love lives of various characters, such as the 23-year-old teacher, who still retains her neko features.
The fighting style in the series is also unique; fighting can only occur between couples (with a few exceptions), where one is the Sacrifice, who receives all damage, and the other is the fighter, who attempts to attack the enemy couple. The pairing system is used by the author to add romance between the two people in each couple. The special kind of battle used in Loveless is called a spell battle, since attack and defense mechanisms are activated by pronouncing certain words -- spell words -- which have a special ability or meaning in battle context. Fighters and sacrifices are united by their names which are given to them beyond their control, possibly before birth. A few examples of pairing names include "Beloved", "Loveless", "Zero", and "Sleepless." Those who go against their name to battle alongside a person of a different name suffer ridicule from other teams and a large loss in battle strength. It is suggested that people are born in pairings and that they don't form a pairing after they meet, therefore the naming system; the bond between two persons is something that is decided for them before they have the ability to make a different choice.