Kanako Miyamae enrolls into the the all-girls school, Ame no Kisaki. On the way to the Girls Dorm she meets a girl named Shidō Mariya with her maid, Shinōji Matsurika. However, Kanako later discovers that Mariya turns out to be a boy. With Kanako's knowledge of the fact that Mariya is a boy, the former roommate of Kanako (Ryuuken Ishima) is replaced by none other than Mariya himself.

It's the first day of school for Kanako. After a troublesome morning with her roommate Mariya, she goes to the class without having any breakfast. Afterwards a welcome speech is held by Mariya and the school student council.

Mariya lends Kanako his rosary which is of great value. Unfortunately, she leaves the rosary in the classroom. As she went back to get it, three girls, who are fans of Ryuuken and are jealous of Kanako because she is on good terms with her, found it and threw it out of the window. Kanako runs outside to search for the lost rosary. On the same day, Ryuuken tells her that she will protect her.

Ryuuken held her promise and "protects" Kanako. She always stays beside her and attends classes together with her, although she is a class above Kanako. She even stays overnight at Kanako's room. But Ryuuken's protection causes Kanako more pain than ease. A classmate of Kanako (Kiri) notices it and to help her, she tells Kanako that they are going out.

Kanako tries desperately to become friends with Kiri. Therefore she asks her Sachi for help. The dorm mistress checks the rooms of the girls for forbidden items. Afterwards, she piles them up on a table and judges how good an item was hidden. Amongst the things found, Kanako's bag, which has a live unidentified mysterious animal residing in it, is also there. She is then told to hide it again, and if she passes the supplementary test, she can then keep it.

The physical examination will be held this afternoon. However, in spite of Mariya being a boy, he attends the examination and Kanako finds out what's behind Mariya's attendance at Ame no Kisaki. Shizu, Mariya's twin sister, makes her debut in the series.

Yuzuru notices that Kiri and Sachi are getting along very well. Because of that, she gets jealous and thinks that Sachi could become better friends with Kiri than she is with her. She starts to act strange towards Sachi and Kiri. It turns out that Sachi was helping Kiri to pick a birthday present for her. Afterwards, all of them (together with Kanako, Masturika and Mariya) celebrate Yuzuru's birthday.

The Virgin Mary Festival is going to be held. After Kanako was voted to be a member in the planning committee, she asks the student council president for advice because she doesn't know much about the festival.

The Festival's preparations are almost reading and the festival is about to begin. It is also revealed how Ayari's (the student council president) and Mariya's relationship soured years ago. Kanako is told of the current seven mysteries of Ame no Kisaki. After asking her teacher, Kuma, about them she learns about the original six ones. She is also told that if she knows all seven, something terrifying will happen to her. After Mariya told her the seventh one, God appears. It is also revealed that Kanako was the cause of many of the seven mysteries around the school, due to her constant explosive nosebleeds.

Kanako has failed in several subjects in the mid-year examinations, so she has to take the supplementary exams. She decides then to study very hard. It turns out that before the exams Kanako was constantly distracted by Mariya, who decided to act like a roommate to Kanako for once and subsequently led to her failures. Thanks to Matsurika's sleep-hypnosis techniques, Kanako almost boycotts the exam and nearly fails again. However, she manages to pass all the exams. Yet, her troubles don't end as she's punished by God for not having passed the exams the first time round. Kiri is given a love letter by a man on a train. It turns out that the man is way older than her and she has no interest in him. Kanako, Yuzuru and Sachi try their best to find a way to reject the man's advances.

A new character is introduced—Father Kanae. He seems to have a crush on Mariya (not knowing that Mariya's a boy) and Matsurika, although he is twenty-seven and a teacher there. Mariya later lies that Kanako's "elder brother" died of the "Tchaikovsky syndrome" in B-minor. He asks him to help Kanako because Kanae reminds Kanako of her brother. In actuality, Kanako hasn't got a brother. So Father Kanae tries his best to help her. Unfortunately Kanako is allergic to males and he inadvertently (and unknowingly) causes her great suffering. He later falls in love with Ayari as well.

It's finally summer and so the swimming sessions begins. Kanako is very excited because at the swimming lessons she can see all the girls in their swimsuits. But during the fact that she daydreams and father Kanae interrupting (even once being out for the whole day because of food poisoning by way of eating raw liver), she collapses very often and because of that has to stay in bed. But she can go to the pool after all before the summer break begins and there she tries to reveal the fact that Mariya is a boy. However, it is revealed that Mariya got his twin sister, Shizu, to take his place.