The story begins with Izumi Hayato running to be student council president. But when a beautiful girl swings in promising the liberalization of love while flinging condoms into the audience, he ends up losing to her and becoming the vice president. At the student council meeting, the newly-elected president invites herself over to Izumi's house, where she promptly announces she is to become Izumi's wife thanks to an agreement—facilitated by alcohol—made between their parents when they were only 3. (Source: MAL Scanlations)

After the death of his parents, Yuuto Amakawa lives a pretty ordinary life in the city. The only problem he has to worry about while attending school alongside Rinko, his next-door neighbor, is his cat allergies. That all changes on his sixteenth birthday, when an Ayakashi—a supernatural creature—attacks him for the sins of his ancestors. Luckily, he is saved by Himari, a mysterious cat-woman with a sword, who explains that Yuuto is the scion of a family of demon-slayers, and she is there to protect him now that the charm that kept him hidden from the supernatural forces of the world has lost its power. Omamori Himari chronicles Yuuto's dealings with the various forces of the supernatural world, as well as the growing number of women that show up on his doorstep, each with their own dark desires. Will Yuuto be able to adjust to his new exciting environment? Or will the ghost of his (ancestor's) past catch up with him?

Hayato Izumi, an introverted and studious high school student, is running for the position of student council president. However, his ambition is soon shattered by his rival, Ui Wakana, an outgoing person focused on the noble goal of improving school life through love and sex education. Accepting his loss, Hayato takes on the role of vice president. Shortly after the election, Hayato is met with a surprise: Ui announces that she will be moving in with him—as his wife! Although initially hesitant, Hayato discovers that this marriage was arranged by their parents, and he eventually complies. Now that they are welcoming a new beginning, the couple must learn how to live with each other while keeping their unconventional relationship a secret from the entire school.

Short specials included in the Onii-chan Dakedo Ai sae Areba Kankeinai yo ne Blu-rays and DVDs.