Ash is a student at Ansalivan Dragon Academy, attended by children who have formed contracts with dragons. He possesses the "star mark," the sign of a contract, but since his partner hasn't been born yet, he seems insignificant. The awakening of the dragon he's raising inside his body is triggered by an incident, and it emerges in the form of a young girl.
Since ancient times, Japan has upheld the tradition of the 12 Zodiac signs. Eto-musumes (Zodiac girls), who have the appearance and behavior of the animals of the Zodiac, are pure hearted messengers who act as a bridge between humans and the gods. Every 60 years, the “ETM 12” tournament takes place in Tokyo’s Akihabara district, where aspiring girls from all over Japan gather for the chance to become the next zodiac sign.
Yoshitaka Nakabayashi, a 14-year-old millionaire who got this huge inheritance after his parents died in an accident, found himself needed to be taken care of and tried to hire live-in maids to do the job. Two runaway girls, Izumi Sawatari and her younger sister Mitsuki, stumped into Nakabayashi's mansion and got hired by Yoshitaka immediately, for Yoshitaka is not only a rich boy but also a pervert with uniform fetishes, who wants to be addressed as goshujin-sama (master). Having nowhere else to settle down along with Mitsuki's pet alligator Pochi, Izumi accepted the job reluctantly.
The story follows Issei Hyōdō, a dim-witted, lecherous second-year high school student who is killed by a girl on his first date ever. Issei is reincarnated as a devil, and from that day forward, he serves as an underling of Riasu, a high-level devil who is also the prettiest girl on Issei's campus.
Dreaming of becoming a hero and vanquishing the Demon King, Raul Chaser enters the Hero Training Program in pursuit of his ambition. However, when the Demon King is defeated and peace returns to the world, the Hero Training Program is suspended indefinitely, making it impossible for anyone to become a hero.
Two years later, Raul reluctantly works at a small electronics store called Magic Shop Leon. Though the former hero-in-training is plagued by the mundanity of working in retail, everything changes with the arrival of a new hire. Appearing at first to be just a boy with good looks, "he" turns out to be a female demon by the name of Fino Bloodstone. She is not just any old demon either—Raul's new coworker is in fact the daughter of the late Demon King! Handed the responsibility of training this eccentric new employee, Raul soon finds his life becoming livelier than it ever was before.
Seven schools are constantly "at war" with each other, and the students within—both male and female—have become skilled fighters and constantly battle with rival schools. Their lives and fates are guided by strange jewels that contain the spirits and destinies of warriors from the Sangokushi period. One girl, Sonsaku Hakufu, has recently moved to Japan and is apparently destined to unite the schools as her counterpart united seven countries long ago. But, like all heroes, there is a darker side to her fate, and as always there is a constant struggle by those around her to break the chains of their own destinies and make their own lives.
Loosely based on the novel "Romance of the Three Kingdoms", modern day Japan sees a similar struggle for power between different rival schools with the three strongest being: Kyosho Academy led by Sousou Moutoku, Nanyo Academy by Sonsaku Hakufu, and Ryuubi Gentoku from Seito High School. Together these three tousei, each with their own mangatama, fight for the honour of becoming ikki tousen and fulfilling their fated destiny through battle and conquest.
Preparing for the battles to come, tournaments and to fight against new opponents from over the world, Hakufu is working to have enough money to make her dream true. But she doesn't consider that old and new allies and enemies will come to scene, and also being a weak leader to the eyes of her companions. A sister also appears. She doesn't even know her mom's past so better to start from the local stuff before attempting to go worldwide.
The main fighters are summoned to a tournament that involves the heads of all the schools. But some of the heads send their trust fighters in their place. They don't realize that the tournament is just the face of a conspiracy to take over the clans. Hakufu now has a disciple as crazy and skilled as her and due to her laziness the disciple ends on the tournament in the place of her master. Now they must prove that the destiny imposed by the souls of the fighters living in their own is not always an absolute law.
Asano begins work as the housekeeper for the old family of Shimazu, where he meets the ill-mannered, selfish, beautiful Sakaya. She is actually the 37th head of the Shimazu family in charge of sealing away monsters with Spirit Archery. Discovering that he has the powers of "true names" and "true eyes,"Asano becomes wrapped up in Sakaya's battle with the monsters as her assistant.
A chibi robot doll appears in the room of a typical high school boy. The robot claims the boy as her husband and then a beautiful girl comes out of the doll's mouth who knows the boy from 10 years prior and had been promised his hand in marriage.
Tokiha Mai and her sickly younger brother, Takumi, have received a scholarship to attend the prestigious Fuuka Academy. On the way, the ferry they are travelling on becomes the site of a destructive battle between two girls wielding apparently supernatural powers. This is only the beginning of their troubles, as Mai learns that she herself possesses these powers - the powers of a HiME.
Takeru Ohyama, a young normal yet perverted minded guy, got accepted and now goes to a school that, unknown to him, was where combat and magic is used. On the first day, he meets again after three years: Haruko Amaya, his childhood friend, Inaho Kushiya, a girl who says she's his fiance, and Kodama Himegami, a blonde who wants to kill him. Finding out that there are many girls there that just don't like him, he is told that everyone there uses a special magic ability while using an item or weapon called a Maken. Later, he finds that no Maken is acceptable for him and doesn't know what to do, since in this school the students get into duels that showcase their magic and combat power, of which he seemingly has none.
Miss Kobayashi is your average office worker who lives a boring life, alone in her small apartment–until she saves the life of a female dragon in distress. The dragon, named Tohru, has the ability to magically transform into an adorable human girl (albeit with horns and a long tail), who will do anything to pay off her debt of gratitude, whether Miss Kobayashi likes it or not.
Takayama enters the training program of JNR with the ambition of becoming one of the venerable train company's engineers. As a trainee he is teamed up with fight-ready Sakurai and stolid Iwaizumi and fellow Haruka Kōmi who has encyclopedic knowledge of trains. Together they learn how security officers for the train line work and get involved in more than one tricky situation.
A girl named Mitsuki Kanzaki lives with her step-brother Yuya after her mother remarries. One day, Mitsuki is possessed by the self-proclaimed spirit of a young girl, Hiyori Kotobuki. Hiyori (in Mitsuki's body) must fall in love with Yuya to move toward the "Gates of Heaven."
Chihiro Furuya, who loves zombies above all else, meets the sweet girl Rea Sanka by chance, and he ropes her into "resurrecting" his dead cat. But then Rea claims she actually has become a zombie, and asks him to take responsibility for it.
The Yūki's residence is now full of people: in addition to Rito and Mikan Yūki, Lala, her twin sisters Nana and Momo, and Golden Darkness. Momo, who also falls for Rito, actively tries to create a harem for him. Meanwhile, a mysterious red hair girl named Mea Kurosaki enters Sainan High School with a hidden agenda.
Kasuga Arata lived a normal life together with his childhood friend, Hijiri Kasuga, in a small town. However, everything changed on the day of the Black Sun, and a magus (mage) appeared before him. The Black Sun caused the Breakdown Phenomenon which destroyed the town where he lives. Because of this, his normal life was artificially reconstructed by a grimoire that his childhood friend had left. The appearance of the magus led him to a new life in the Royal Biblia Academy and meeting the members of the Trinity Seven.