Yuzaki Nasa was preparing for his high school entrance exams one snowy night when he spots a beautiful girl on the other side of the road. Feeling somewhat drawn to her, he walks towards the girl and is severely injured after getting run over by a truck. Despite hanging on for dear life, Nasa still walks over to the girl and knowing this may indeed be his last chance, confesses his feelings for her. She replies, “I’ll go out with you if you marry me.” Nasa immediately agrees but then loses consciousness. A few years later, he keeps busy at his part-time job, believing they’ll be reunited again someday. One day, someone randomly shows up at his doorstep. It happens to be the girl he shared that fateful encounter with.

Nasa and Tsukasa have submitted their marriage registration. As the newlywed couple approaches their first night together, they realize Nasa's apartment doesn't have enough necessities for two people, leading to Tsukasa suggesting she spend the night at a hotel. But Nasa stops her, and proposes they go shopping instead. After returning home, Tsukasa sleeps relaxedly while Nasa is tense with excitement from seeing a new side of his wife.

Nasa and Tsukasa's newlywed life has finally begun. The two of them head to a bathhouse run by a girl who went to middle-school with Nasa, Arisugawa Kaname. Kaname is shocked to see Nasa with a girl, and is curious about what happened after learning about the marriage. Meanwhile, Tsukasa heads into the bath and encounters Kaname's sister Aya. When she asks Tsukasa about her connection to Nasa, Tsukasa replies that they are family.

As Tsukasa waits for Nasa to return home, a young girl named Chitose, who calls her "Nee-sama" confronts her. Chitose asks for Tsukasa to come home with her, and after being ignored, encounters Nasa. He tries to cheer her up, but after learning that Nasa is the one married to Tsukasa, Chitose's attitude suddenly changes. As Nasa tries to explain, Chitose shoves him into a black car that then drives away.

During the ruckus as the Kaginoji house, Nasa and Tsukasa pledge their love to each other at a church. After Nasa reports to Kaname that he has finally proposed, she points that he still doesn't have a ring. Although he doesn't take much notice at first, Nasa gradually becomes more self-consciousness about the role of a ring in newlywed life.

Nasa realizes he's been so enthralled with newlywed life he forgot to tell his parents he's gotten married. He tries to wrap it up with a simple phone call, but Tsukasa decides she wants to meet his parents. While Nasa is anxious about a potentially embarrassing meeting, the two of them head to visit Nasa's parents in Nara.

Nasa and Tsukasa take an overnight bus to visit his parents in Nara. They attempt to enjoy the trip like a honeymoon, when Chitose shows up at a service area, asking to know why Tsukasa married Nasa, who happens to overhear the conversation and begins to wonder the same thing. As the couple attempt to enjoy seeing the sights in Kyoto, Chitose appears again. She attempts to test Nasa to see if he's worthy to be married to Tsukasa, and he explains why he decided to marry her.

Nasa and Tsukasa arrive in Nara and head to the Yuzaki family's house. Despite demanding to meet Tsukasa, Nasa's parents, Enishi and Kanoka, are both clearly nervous. And not long after introductions, Enishi ends up making a deal with Tsukasa.

After returning from Nara, Tsukasa and Nasa find themselves without a home thanks to a freak lightning strike. Nasa's prepper habits keep the damage to a minimum, but they still find themselves temporarily homeless, until someone offers to let them stay in a spare room. And so, the newlyweds begin their stay at the Arisugawa house.

Nasa and Tsukasa are now enjoying newlywed life as guests of the Arisugawa family. Things proceed normally until they receive a call from Nasa's previous landlord, offering them an apartment at a newly constructed building. The two of them go to check out a showroom of their potential new home, arriving at a high-rise apartment building.

Nasa suggests takoyaki party to the Arisugawa sisters so that everyone can get to know each other better. Meanwhile, Chitose tracks Tsukasa down to the bathhouse. The game-loving Aya finds herself getting along with the two of them, and before long competitive sparks start flying!

Nasa comes down with a fever while at work. Despite his claims of being fine, Tsukasa takes him to the hospital and starts to nurse him back to health. After recovering, the two of them head to a summer festival. When Nasa begins to wonder about how many people out there worry about him, Tsukasa has something to say.