Yumeko gets transferred to second year "cherry blossom " class and is assigned Ryota Suzui, the class representative with personally giving her a tour of the academy.
While showing her around the academy, Yumeko observes the tag around Ryota's neck that indicates he's a "pet" after losing a gambling match against Mary Saotome and owing to her a debt of 5 million yen that he has the inability to pay off.
Ryota becomes flustered at Yumeko's closeness and moves away before asking her if she's ever gambled before. To which she replies that she understands the basic rules of some gambling games. Ryota tells her that gambling at the academy is almost considered a tradition and that after school many of the class and club rooms turn into gambling dens. He warns her that there are a lot of rich students at the academy who have infinite amounts of money to gamble with and that she needs to be careful or else she'll be entrapped in one of their games.
Yumeko begins to laugh causing Ryota to look surprised at her reaction; she remarks that the thought of such sort of gambles sounds fun.
Yumeko is then shown surrounded by many of her female classmates when she returns to class as they bombard her with personal questions. Mary introduces herself to Yumeko and invites her to a gambling match after school, much to the concern of Ryota. Yumeko accepts and the classroom is then swiftly changed into a gambling den with she and Mary sitting in the middle of the room facing each other and their classmates surrounding them.
Yumeko asks Mary what game they should play. Mary suggests they play "Vote Rock-Paper-Scissors," an original game that was created by the class in which students draw a rock, paper, or scissors onto a card that is then placed into a sealed, metal box that prevents the players from seeing what's on them. Mary then goes over the rules as she and Yumeko draw 3 cards each out of the metal box and pick one card out of their hand to play. She then further explains that if they get a tie, they must pick one of the other 2 cards they have yet to play. If they get 3 ties, then the set is a draw and they have to play a new set. Mary reveals that the game isn't like normal Jankenpon where a player has the ability to choose whatever move they want, but the game relies on the ability to read the flow of the game.
Ryota attempts to protest the game, but Mary grabs him by his tag and coldly tells him to bring them some poker chips. Mary gives Yumeko 120 chips that, individually, are worth 10,000 yen each that totals to 1.2 million yen. Mary tells Yumeko that she can set the bet of the game so that they can begin. Yumeko starts the bet with 2 chips (20,000 yen) as their classmates beginning filling out cards.
Ryota narrates that it's pretty rare for a player to get 3 different cards, but that the likeliest of outcomes is for a player to receive either two rocks and a paper and depending on the frequency of a card that appears then it's safe to assume that that image appears the most in the box. And that the game is played on the uncertainty of either opponent.
Mary and Yumeko draw their first card, with Mary producing a scissors card and Yumeko producing one that shows rock. Yumeko gets the first win, to which Mary congratulates her on. As a result of this, Yumeko takes 2 of Mary's chips, thus winning her 20,000 yen. Continuing the game, Yumeko then bets 50 chips (500,000 yen) much to the shock of Mary and her classmates.
A new set begins with the first draw ending in a tie, however, the next draw ends with Mary winning the 500,000 yen bet. Mary exclaims her elation at winning such a huge bet and a new set begins. Yumeko again bets 2 of her chips and wins the next draw of the new set. Yumeko then bets again 50 chips which cause a new wave of shock to erupt in the class. Mary wins the set, giving her a total of 1 million yen that she's made in winnings.
Mary insists that they keep playing the game and when she gets no response or reaction from Yumeko, cruelly taunts her that it seems like she's getting cold feet after having lost 1 million yen. Yumeko calmly replies that the game is only just getting started and bets 2 chips. This causes Mary to stifle her laughter as Yumeko only has 24 chips (240,000 yen) left compared to her own 216 chips (2.16 million yen). The two of them continue to play until Mary remarks that Yumeko has lost all of her chips.
Yumeko then asks Mary if she's willing to participate in one more game. This surprises Mary but worries Ryota who's concerned that Yumeko will rack up a debt that forces her to become a pet. Mary agrees to another round and begins to cruelly taunt Yumeko off camera. Yumeko reaches for her school bag and opens it, dumping stacks of yen onto her desk before she places down a bet of 10 million yen. This shocks everyone, especially Mary who is concerned that Yumeko is carrying that much money on her. Mary berates Yumeko and tells her that there's no way she can bet so much of her own money on a single game.
Yumeko's eyes change to a crimson color as she remarks that making such high-risk bets on a single game is what makes it fun. She remarks that madness is simply the essence of gambling and that in a capitalist society, money is the ruling force and synonymous with one's own life. Because of this, a sane person wouldn't entrust their entire life to luck, but yet people go to casinos because they derive pleasure from it. And as a result of this, gambling becomes more fun the crazier it gets.
In the student council room, the president receives a report about the new transfer student. The president, interested, remarks that there's now a snake within their paradise.
Mary, still in the classroom with Yumeko and their classmates, stands up from her desk, refusing to participate in the gambling game anymore. Yumeko taunts her with her own words; asking her is she's gotten cold feet. This infuriates Mary's pride who decides to play the new round.
Yumeko laughs as she comments that high stake games are fun to which Mary questions if Yumeko even realizes how high the stakes of the game truly are. Mary reveals in an inner monologue that she has 21 out of 30 students in the classroom are rigging the game in her favor either with the hopes of increasing their own social status or do them owing her a debt of some sort. Confident because of this trickery, Mary believes that she'll win the game.
Mary asks Yumeko if she's ready to begin the game, but gets no response as Yumeko is seen staring at her cards. Mary tells Yumeko that they're only holding 3 cards in her hand, so there's not much stalling she can do to prolong the inevitable outcome of the game. Yumeko then reveals to Mary, that she knows about her rigging the game in her favor and that most of the students are working for her. This shocks Mary and causes a stir to erupt in the class. Yumeko deduces that not all of the students can be in her pocket as there has to be a portion of them that would assure her victory and that Mary didn't do a good job of hiding signs that the game wasn't in her favor. During two games where Yumeko bet 500,000 yen, Mary played the same cards twice, which convinced Yumeko that she was up to something. However, when bets of 20,000 yen were being placed, Mary made sure to mix the cards well. Yumeko states that Mary can't fool a single person that they aren't being conned if she herself isn't prepared to lose money.
Shaken by this, Mary convinces herself that Yumeko's "smack talk" won't disturb her confidence in the rigged game. A tense moment settles between them as both of them produce their drawn cards. A look of pure disbelief is seen on Mary's face as she draws a paper and Yumeko produces scissors, revealing to her that she lost the game allowing Yumeko to win 8.8 million yen in earnings. Yumeko then asks her to pay up the large sum of money.
Mary still in disbelief, struggles to come to terms with the outcome of the game and reveals that she wanted to win and force Yumeko into debt and eventually into servitude as a "pet," the same thing she did with Ryota. Mary tells Yumeko that she's incapable of producing such a large quantity of money to pay her back, but asks for an extension period of a few days to amass it.
Yumeko walks away while telling Mary that she had a fun time so Mary's debt to her is now null and void and tells everyone to have a nice day before leaving the classroom.
Yumeko is walking through the academy halls when Ryota calls out to her and asks her how she figured out Mary's ruse. Yumeko reveals that it was easy as she knew from the start that Mary was rigging the game and manipulating the votes and as a result of this, all she needed to do was figure out which card would be the most common. But to do this there would have to be some sort of communication system among those who were participating in the ruse, but that Mary wasn't a part of it as she didn't signal out a sign or made any attempt to communicate with those who were helping her. But instead that it was someone else in the class who was giving a signal on what people should draw. Yumeko reveals that she figured everyone was staring at her during the game, but that she was wrong and instead everyone was staring at the person behind her who happened to be Ryota. Yumeko then tells him that once she figured out the ruse all she had to do was figure out what card he was signaling Mary's helpers to draw with the aid of her hand mirror.
Seemingly relieved at this, Ryota asks Yumeko how she knew to pull out the scissors card in the last round. Yumeko reveals that it was simply a complete coincidence, it was simply luck.
Ryota reveals that he's planning to drop out of the academy due to his inability to pay off his large debt that he owes to Mary and others. Ryota remarks that he wishes he had Yumeko's confidence and bows to her in apology. Yumeko gives him a large stack of cash as a thank you gift that expresses to him her feelings of having a fun time gambling.
Ryota tries to refuse the gift, but Yumeko quiets him and tells him that she hates situations in which she knows her own outcome in a game as it really isn't gambling. Due to this Ryota realizes that Yumeko isn't as normal as she seems, but instead a compulsive gambler.