In the world of Loveless, each person is born with cat ears and a tail, which disappear only if that person engages in a sexual intercourse. Because of this, they have come to symbolize virginity and innocence. Additionally, fighting is only done by "fighting pairs" or couples, where one is known as the Sacrifice and the other as the Fighter. The first receives the damage while the latter attacks. Ritsuka Aoyagi is a 12-year-old boy, who for some unknown reason suffers from amnesia. His brother got killed recently, and as if his life has not been hard enough lately, on his first day at the new school he gets approached by a stranger called Agatsuma Soubi, who claims to have known his late brother. Ritsuka finds out that Agatsuma and his brother used to be a fighting pair, and that Agatsuma has inherited Ritsuga now that his brother is gone. Together, they try to find the truth behind his brother's death and the organization known as the "Seven Moons," which may have been responsible for it. All the while, it seems that Ritsuka and Agatsuma are becoming closer than they intended to be…

Yoshikazu Miyano's troubles first start one hot summer day when Shuumei Sasaki steps into his life. Sasaki saves Miyano's classmate from a group of bullies, and after that, Miyano cannot seem to shake off his eccentric upperclassman. His silent admiration for Sasaki gradually sours into annoyance each time the so-called delinquent refuses to leave him alone. Constantly being called by cute nicknames and having his boundaries ignored, Miyano wonders why Sasaki wants to get close to him. The shy and easily flustered Miyano harbors an embarrassing secret—he is a "fudanshi," a boy who likes boys' love (BL) manga. The last thing he wants is for other students to find out, but through a slip of the tongue, he reveals the truth to Sasaki. Intrigued, the clueless Sasaki asks to borrow a book to read, which he is given very reluctantly. To Miyano's surprise, Sasaki enjoys the BL that he receives and asks for more, marking a shift in their strange dynamic. Although Sasaki appears to possess some personal agenda, his feelings for Miyano become complicated the more time they spend together. As they now share a common interest, their relationship is poised to change and further develop. [Written by MAL Rewrite]

After having to deal with jealousy from his co-workers for working under his father's name, prideful literary editor Ritsu Onodera is determined to establish himself in the industry. To accomplish this, he quits his job at his father's publishing company and transfers to Marukawa Publishing. But instead of being placed in their literary division, Ritsu finds himself working as the rookie manga editor for the Emerald editing department, a team that operates under extremely tight schedules in order to meet deadlines. There, Ritsu is introduced to the infamous editor-in-chief Masamune Takano, a persistent man who strives for results. As it turns out, Takano is actually Ritsu's high school love, and it is the aftermath of that heartbreak has caused Ritsu's reluctance to fall in love again. Now with the two reunited after several years of separation, the reestablishment of their relationship is marked by Takano's vow to make Ritsu say that he loves him again. Sekaiichi Hatsukoi follows three couples that are interconnected within the manga industry, with each being subject to the budding of first love. [Written by MAL Rewrite]

Misaki Takahashi is a regular high school student who is preparing for his university entrance exams. In order to reduce the stress of studying, or so he hopes, he accepts the help of his older brother's best friend, and famous author, Akihiko Usami. However, Masaki is about to find out that Usami's books are of a very naughty genre, and that there may be something naughty waking up inside Masaki as well. Junjou Romantica also follows the story of two other couples loosely connected to Masaki and Usami's "Romantica." Egoist shows the very passionate, but often complicated, relationship between university professor Hiroki Kamijou (whose life has reached an all time low) and paediatrician Nowaki Kusama, who falls for Hiroki at first sight and would do anything to make him happy. The third story, "Terrorist," shows just how obsessive love can become when rich eighteen-year-old Shinobu Takatsuki finally discovers something that he cannot have so easily—the literature professor You Miyagi. There is passion abound as these three couples try to achieve their goals in life while also falling into temptation and anguish with their partners.