Although the city of Fukuoka might look relatively peaceful at first glance, in actuality it houses a thriving mixture of dangerous individuals such as killers, detectives, and professional revenge seekers right beneath its surface. Among their number is Zenji Banba, a laidback and observant detective who is investigating the work of other hitmen companies in the area. However, Banba might not be the only one with a bone to pick with these organizations, as Xianming Lin, a crossdressing male hitman in the employ of one such company begins getting fed up with his lack of jobs and pay. One day, after Lin's current target commits suicide before the hitman could reach him, his company refuses to pay him even half the amount they were originally supposed to for the assassination. Frustrated, Lin requests another mission and is offered the job of taking out Banba, whom his organization believes has been interfering with their business. However, when Banba arrives at his home and finds the hitman inside, Lin surprisingly doesn't even attempt to kill him. Instead, he offers the detective another option: to join him and form a team. With the offer on the table, exactly how will Banba respond, and just what plans does Lin have in store for the underground world of Fukuoka?

Homeless and fresh out of employment, Mito Yamamoto faces familiar loneliness and despair. Luck is simply not on Mito's side; when he stumbles upon a cafe and cuts his hand, a strange server named Ruka Saotome licks the blood from his wound and even dramatically retches at its apparent disgusting taste. Offended and dispirited, Mito runs off to a bridge, hoping to put an end to his misery. But when Mito accidentally slips, he is miraculously saved by Ruka, who reveals he is a vampire. Unable to drink blood from just any woman for mysterious reasons, Ruka proposes that Mito become his thrall—a vampire's human servant and primary source of food. In this deal, Ruka will shower Mito with love to sweeten his blood, and Mito will gain a warm place to call home. However, there is an issue: Mito is a girl! Concealing her long, flowing hair and feminine body, Mito readily takes this chance and enrolls in the Hijirigaoka Boys' High School while working part-time at the cafe with Ruka. But the more Mito's bond with Ruka deepens, the more she struggles to hide her secret.

Much like the other students at her school, first-year student Saki Aoi finds herself captivated by the beauty of her senior on the school board, Makoto Hanaoka. While she worries that Hanaoka would be uncomfortable receiving a confession from another girl, Aoi musters up the courage to tell her anyway. However, Hanaoka's response surprises Aoi for a completely different reason—Hanaoka is actually a cross-dressing boy! Fully expecting Aoi to be abhorred by this revelation, Hanaoka is shocked to find that she has no issues with it. Though Hanaoka rejects Aoi's request to go out with her—citing his identity and the fact that he has never fallen in love before—Aoi insists that she will become his first love. Taken aback by Aoi's determination, Hanaoka wonders if he can really fall in love with her if he cannot find it in him to truly love himself first.

Hotaru Tachibana has a strong sense of justice and just cannot help confronting those who choose to perform malicious acts. Furthermore, Hotaru is actually a girl who likes to disguise herself as a boy. After hearing rumors that her best friend was tricked by the popular host of a local club, Hotaru seeks to punish the evildoer. Upon arriving at the club, however, she is challenged to a so-called "survival game" by the host Masamune Matsuoka, where the first person hit by the bullet of a toy gun will lose. After a destructive fight which results in Hotaru's loss, Masamune forces the young "boy" to join his survival game team named Toy Gun Gun, in order to repay the cost of the damages that "he" has caused inside the club. Although she is initially unhappy with this turn of events, Hotaru quickly begins to enjoy what survival games have to offer and is determined to pay off her debt, much to the dismay of Tooru Yukimura, the other member of Toy Gun Gun. As time goes on, Hotaru begins to develop a close friendship with the rest of the team and hopes to take part in realizing their dream of winning the Top Combat Game (TCG), a tournament to decide the best survival game team in Japan. Although Hotaru tries her best, there are just two little problems: she is absolutely terrible at the game, and Toy Gun Gun doesn't allow female members on their team!