When two doors are discovered in an ancient ruin, the gateways to shinkai, the realm of the shinzoku (Gods) and makai, the realm of the mazoku (Demons) are irreversably opened. The races of human, shinzoku, and mazoku come together in the mortal world and nothing will ever be the same. One day, two new families move next door to a boy who had previously been living a very peaceful life. In one house lived the family of the King of the Gods, and in the other lived the family of the King of the Demons. Both families had one daughter whose single wish to live next to the boy they had fallen in love with years ago has just been fulfilled. Also living with the boy is his childhood friend. With these three girls vying for his affections, the boy finds that his new life filled with despair, jealousy, and just a little hope is beginning.
Rin is enjoying a rather normal life living with his childhood friend Kaede due to family deaths on both sides. One day at school, two new classmates transfer into his class: Lisianthus, heiress to the Realm of the Gods, and Nerine, heiress to the Realm of the Demons. Rin is told that he has been picked to marry either one, though it will be his choice as to whom.
After a few days of adjusting to his new neighbors, Rin is starting to find it hard to cope with the recent changes in his life. Eventually, he starts to walk to and from school alone and one day while walking from school he meets a girl named Primula from the Realm of the Demons who is very attached to him, literally. When she comes home with him later, it is decided that she will live in Kaede's house from now on.
Summer is almost here, but first the students must go through their final exams. While everyone is studying, Sia gets some help from Rin, even though it's not much.
During the time when Rin and his classmates are cleaning their classroom, Nerine gets angry at a couple of guys bad-mouthing Rin and manages to nearly blow up the gym. Later, when a picnic is planned where everyone makes their own food to eat, Nerine must get help from Asa in order to learn how to cook.
With the ever-increasing presence of Nerine and Sia in Rin's life, Kaede is beginning to feel left out. When Kaede comes down with a cold, she tries to push herself so as not to be so much of a bother to Rin.
With Rin and Kaede going to school so often, Primula is starting to miss Rin so one day she comes to school unanncounced, though eventually leaves with some coaxing by Rin. Later, it is decided that Primula needs some undergarments she is lacking and thus Rin and the rest of the girls go out to help Primula with this problem. During their outing, Rin buys Primula a new cat doll.
After a popular boy confesses to Asa, she's finding it hard to accept his feelings. After Asa gets injured during PE, Rin walks her home and they're able to grow closer together.
Inspired by a horoscope she read, Sia decides to take the inititve and asks Rin out on a date. However, following the date as she planned it out earlier proves difficult as people they know keep on showing up.
Now that summer's here, Rin and the girls have decided to go to the beach to have some fun. Everything goes smooth for a while, but when Rin and Sia are stranded offshore, what will they do?
After what happened at the beach, rumors start flying around that Rin and Sia are to be wed. As emotions start flaring up, will the rumors turn out to be true?
During the summer break, Mayumi goes to eat at the restaurant Kareha works at, though forgets her wallet, so she must work off her debt for the day. During this time, Rin's teacher is finding it difficult to find a good man to be with.
With the summer almost at an end, everyone is still trying to finish their summer homework before the deadline. Later on, Primula falls ill and Rin learns of her terrible past.
With Primula taken back to the Realm of the Demons, Rin and Kaede try to cope with their missing family member. Ultimately, Primula's condition comes out in the open and the one and only cure is revealed.
After Nerine ran to the nearby park, she tells Rin about the past she had with her clone Lycoris and how it all ties in with Primula. Later, after Asa collapsed at Kaede's house, Rin goes to see her at her own home where Asa tells him some of her own past.
Rin, Kaede, Nerine and Sia have gone to the Demon Realm in order to see Primula again and try to help her in any way. Ultimately, things take a turn for the worse when she starts to lose control of the magic stored in her body. What can Rin do to save her?
While Rin is starting to spend more time with Asa, Sia is starting to feel that she's being left out. With no where else to turn, her other more assertive self surfaces and asks Rin out on a date.
After Sia's other self surfaces, Rin and she go out on a date completely led by Sia herself, with Rin more or less as her captive. How will Rin get out of this awkward situation? Meanwhile, the girls at school start to worry about where he's gone missing.
Rin goes out on a date at an amusement park targeted towards couples which is planned by Itsuki, Mayumi, Nerine and Sia so that Rin would voice how he feels towards Asa.
Rin starts spending most of his time with Asa and completely ignores Kaede. Kaede's past is shown and her yandere personality is revealed.
After Asa suffers another attack, Kaede starts to realize all that she's done in the past few days, but still cannot come to terms with where Rin's feelings truly lie. With almost nothing left, what will she do when told Rin may be leaving her house for good?
Kaede has completely shut herself off from everyone, trying to think on what to do next. Before long, Primula finds that Kaede is gone and Primula runs to Rin to inform him. During her outing, she meets Asa and they have a talk about their feelings for Rin.
Rin has packed up all his things and has already found a cheap apartment to move into. On the day of the move, several of his friends come over and help him out.
After Asa collapses once more, she's rushed to the hospital, though the doctors cannot do much to improve her condition. Asa's mother Ama reveals to Rin a deep dark secret about her past.
Asa escapes from the hospital and goes to the spot where Rin first confessed to her. Before long, Rin goes there to meet her, though there's still not much he can do. When all else has failed, Rin is prepared to do anything to save Asa.