Synopsis Till Now

Yu Isshiki, a college freshman, has been dating Karen Mitsumoto for a year; they attend the same university and move in the same social circle.

One day Yu discovers Karen is cheating on him with a handsome upperclassman from their circle, Tetsuya Kamokura. Driven to desperation, he contacts Kamokura’s girlfriend, Toko Sakurajima, and blurts out, “I want you to cheat with me.”

Toko proposes a different form of retaliation. “If the cheating is a fact, simply doing the same is not enough of a punishment. I will dump him when he is most in love with me, and declare right in front of him that I am ‘spending the night with another partner.’”

So Yu and Toko form a united front to punish their unfaithful partners.

Toko is a beauty known on campus as the “Shadow Miss Campus,” and in high school she was called the “Goddess of the Library.” Yu, Toko, and Kamokura all graduated from the same high school, and Yu has admired Toko since those days.

Yu has two main objectives: to exact bitter revenge on Karen for betraying him, and to repay Tetsuya Kamokura—who stole his girlfriend despite being his senior—twofold.

To achieve that, Yu must be the person Toko claims she “spent the night with” during the final act.

Toko insists they first “secure definitive evidence of the affair.” They recruit their best friends, Yota Ishida and Kazumi Kano, and through Toko’s maneuvering finally catch Karen spending the night at Kamokura’s apartment.

With the affair confirmed, they set the date for “dumping the cheaters and declaring the night spent with another”: Christmas Eve.

Until then Yu must win back Karen’s wavering affection. Toko gives him a plan to make Kamokura cancel a planned “cheating trip” at the last minute so Karen will be disappointed and Yu can “comfort” her. The operation succeeds.

Next, Toko analyzes Karen and decides she craves self-display and social approval. She tells Yu to “increase his popularity among the other girls,” reasoning that Karen would feel a greater loss if Yu were prized by others. Toko orchestrates opportunities for Yu to interact with the key female members of the circle; his reputation among the girls rises, and Karen begins to take interest in him again.

Meanwhile Toko wrestles with an insecurity—wondering if she lacks girlish charm. She asks Yu to teach her “what makes a girl cute from a guy’s perspective.” Their first attempt ends with Yu offering only clichés, which disappoints her. He asks for a second chance and takes her on a full-day date, photographing moments he finds genuinely charming. Seeing those snapshots helps Toko recognize her own appeal, and the two grow closer.

Finally Christmas Eve arrives. The circle holds a party where a “Best Couple” is chosen by vote, the prize a stay at a bayside hotel. Tetsuya Kamokura and Toko are voted Best Couple, but thanks to a scheme by the emcee, Kazumi, the hotel voucher is awarded to Toko personally.

In front of everyone Toko calls Yu forward, announces she is breaking up with Kamokura, and Yu declares his breakup with Karen. When a furious Kamokura demands a reason, Yu says, “Because you were cheating with my girlfriend, Karen!”

Karen at first denies it, but faced with a mountain of evidence she snaps and storms out. Kamokura insists he won’t break up with Toko, but he cannot answer her final question. Toko leaves the party with Yu.

They enter the bayside hotel; Yu is a bundle of nerves while Toko remains composed. “You’re actually going to date me, right?” he asks, and they both agree to make their relationship real.

“We stay here like this until midnight.” As Toko promised, they spend the evening together without anything physical. Just before midnight she says she has to leave because her father has come to pick her up, and explains, “We only needed Kamokura and Karen to believe we spent the night together. I never intended to actually do anything.” She adds, “I have no intention of having intimate relations until marriage. I never had a physical relationship with Kamokura, either.”

With those words she leaves the room. Only then does Yu realize the depth of what they’ve done: the revenge he sought against Kamokura was far greater than he’d ever imagined.