In Yumeko's first day at Hyakkaou Private Academy, she learns of the school's dog-eat-dog ways the hard way. Hoping to increase her position at the school, a student in her class, Mary Saotome, challenges Yumeko to a modified game of Rock-Paper-Scissors. In this game of Rock-Paper-Scissors, the other students in the class draw rock, paper or scissors and place it in a ballot box. Even more, a game of chance than your standard game of Rock-Paper-Scissors, what you can throw is determined by the cards you draw from the ballot box.

Yumeko and Mary each start the game with 120 chips, worth ￥1,200,000 total. In the first round, Yumeko makes and wins a meager bet of ￥20,000. In a completely foolish and naïve manner, she then bets ￥500,000, which she promptly loses. After another series of winning a two-chip bet to lose a fifty-chip bet, Yumeko finds herself at the whim of Mary's cruel side as she is taunted. Despite the chip count and Mary's taunting, Yumeko states that the game's just beginning. Even with all her confidence, Mary wins all of Yumeko's chips in the end.

Almost as if she didn't suffer a crushing and humiliating defeat, and much to everyone's surprise, Yumeko then asks Mary to play one more game. When Mary comments on her lack of chips, Yumeko then empties ￥10 million from her bag onto her desk. When Mary expresses her disbelief at Yumeko's willingness to put ups such a large sum of cash, Yumeko taunts her in return and reveals that she's aware that Mary has rigged the game in her own favor. For Yumeko, the thrill of gambling is more exciting than winning, which is why she goes all immediately, leaving it all up to luck.

After receiving an invitation to the Traditional Culture Research Society club room, Yumeko finds herself facing Yuriko Nishinotouin, a member of the Student Council and president of the Traditional Culture Research Society. There she is challenged to an original game, Life or Death.

In the game Life or Death, players place bets on where they think miniature swords in a metal cup will land. In this deadly game of roulette, picking the correct number, however, does not guarantee a payout. If the sword lands blade down, then the player will receive 30 times their bet. If it lands blade up, however, the player will lose 30 times their bet. With such extreme stakes, Yumeko gleefully agrees to a game.

The first-round ends in a draw, as no player correctly guessed where the swords would land. In the second round, unlike the last, Yumeko places all of her chips on the number, hedging her bets that she has figured the game out, more specifically how Yuriko is cheating. As Yuriko realizes that she has been caught in her cheating and begins to panic, several members of the Student Council, including the President, come to observe the game. When the dealer lifts the cup, it is revealed that while Yumeko had correctly guessed where the sword would land, it landed in the death position, leaving Yumeko with a ￥310 million debt.

Despite the large debt and suspicions that there was, even more, cheating involved than she initially thought, Yumeko becomes even more excited about her time at Hyakkaou Academy. Yumeko made her most extreme bet, both in terms of thinking she'd understood the limits of her opponents cheating as well as in monetary terms. For her miscalculations, Yumeko found herself classified as a Mike, someone needing to make even more extreme bets to overcome her insurmountable debt.

It wouldn't be any fun if students in large debts are stuck there without any real chance to get out of their debt. To give these students a shot at clearing some of their debt, the Student Council announces a Debt Exchange Game. In this game, 4 players with a debt will play 10 rounds of two-card Indian Poker. At the end of the rounds, a player's debt will be replaced with that of the person who was originally in their ranking, with the winner of the game's debt being cleared completely.

Yumeko finds herself in the same group as Mary, along with another Mike, Nanami Tsubomi, and the tough and arrogant Jun Kiwatari, who pretends to have a ￥10 million debt in order to make a profit from the game. The first few rounds are played quite normally, until the third and fourth round. After Yumeko wins a hand with a higher on suit-hand than Jun, and Mary bets in the same fashion the following turn, Jun folds, thinking that Mary and Yumeko are working together to let each other know their hands, only for Mary to reveal that she didn't have a winning hand and was actually bluffing.

Yumeko and Mary then reveal that they are, in fact, working together, just as Nanami and Jun are, to supply the other with information. With the players now actually aware of their hands, the game becomes a game of bluffing. By the final turn, Jun has bluffed his way into first place, but when Yumeko and Mary make bets that would give Nanami first place if she calls their bet. Nanami calls the bet, betting not only her chips but also her position in the school's hierarchy. While Yumeko, with the largest debt, had nothing to lose, the other students risked increasing their debts for the chance to lessen or even erase it completely: a pretty extreme bet considering how deep in the red many of them were, to begin with.

After learning of the school's hierarchy and pet system from her friend, Ryota, Yumeko become even more excited about having transferred to Hyakkaou. So excited, in fact, that she challenges a member of the Student Council, Itsuki Sumeragi to a game. Short on cash, but excited to gamble against one of the strongest gamblers in the school, Yumeko accepts a ￥20 million loan from Itsuki for their game of "Double Concentration." In Double Concentration, Yumeko and Itsuki must find matching cards from not one, but two decks of identical playing cards.

The first round is remarkably close, with spectators realizing that in order to find matching pairs with such efficiency, Yumeko and Itsuki must be memorizing the location of the cards that they've already flipped. After a close series of turns, Itsuki manages to take the lead and close out the game, leaving Yumeko with a ￥20 million debt. Realizing that she can't pay back this debt, Yumeko begs Itsuki for another game, hoping to win their second game, and break even.

Instead of ￥20 million, Itsuki has a more interesting wager for Yumeko: Itsuki is a fan of nails and has an amassed a collection of human nails through gambling. Itsuki agrees to a second game of Double Concentration with Yumeko on the condition that she bets her nails. Yumeko agrees to the bet, and wins in one turn, revealing that she was aware of how Itsuki cheated in the first game. Yumeko then decides to raise the stakes one last time, challenging Itsuki to a different card game, where the loser will experience the pain of having their fingernails ripped off. Unfortunately, Yumeko is clearly made of a different cloth, as Itsuki tearfully declines the challenge.

After the Student Council President takes a surprise leave from the school, the Student Council Head of PR and idol, Yumemi Yumemite, decides to be the next member of the Student Council to challenge Yumeko. With the help of Student Council Accountant, Kaede Manyuda, Yumemi decides to play a series of games against Yumeko, set up so that her victory will be ensured.

Before the match, Yumemi invites Yumeko behind the stage to prepare for their post-concert match. During the conversation, Yumemi tells Yumeko that due to them both having "yume," the character for "dream," in their names, it is the fate of them being together. To achieve this, instead of having Yumeko match her bet of ￥50 million, Yumemi decides that if she Yumemi wins, the two will become an idol group, Dreaming Creaming Sisters. When Yumemi states that she is an idol to see the smiles on her faces, Yumeko calls her out on her lie and gets Yumemi to confess that she vehemently despises her fans and that being an idol is just a step on her path to achieving her life goal of winning an Academy Award.

Yumeko then reveals that she planted a recorder on Yumemi's assistant, recording the entire confession. Having revealed her trump card, Yumeko changes the bets so that the wagers are a bit more even, with both girls putting their lives and futures on the line: if Yumemi wins, Yumeko will hand over the recording and give up her life and become a member of Dreaming Creaming Sisters. If Yumeko wins, however, she will play the recording to all of Yumemi's fans in attendance, thereby ruining any chances of achieving that which she's sacrificed so much for, an Academy Award.

For Yumeko, thanks to her position as a Mike, her future is already out of her hands. But for Yumemi, ￥50 million yen, a small amount to her, and her entire life's work is on the line.

After facing the majority of the Student Council, Yumeko finally receives the chance to gamble against the Student Council President, Kirari Momobami. During their conversation, they discuss their love and reasons for gambling. They then agree to one game, with stakes that are of any extreme worth to the two of them: the loser will withdraw from Hyakkaou Private Academy. For Kirari and Yumeko, two lovers of gambling, to leave Hyakkaou Academy would be akin to getting kicked out of Heaven.

Yumeko and Kirari agree on a game of Tarot, where Yumeko gains the value of the card flipped. If the card is facing her, then it has a positive value, if it's facing away, negative. After Yumeko, Kirari, and Ryota each flip a card, if Yumeko's score is positive, then she wins. If the fool card is flipped facing Yumeko, then she instantly wins, however, if it's facing away then she instantly loses. After Yumeko and Kirari each take their turns, Yumeko has a score of –20.

With –20 points, it falls on Ryota to ensure that Yumeko doesn't leave the school. With Kirari having flipped the highest valued card, he realizes that he needs to find the fool card. Ryota panics because even though the bets seem to only affect Yumeko, he wants to be together with Yumeko and has something to lose as well.

In the end a game, three people have something on the line. For Ryota, Yumeko leaving the school would cause him to lose the one important thing to him at Hyakkaou Academy. Yumeko and Kirari risk their lives at Hyakkaou Academy, a punishment second only, perhaps, to death.

As rule of Hyakkaou Private Academy, members of the Student Council cannot refuse a challenge to a Public Match by "Mike"s or "Pochi"s. After having her initial challenge to a game refused, Yumeko invokes her right to a Public Match with Kaede Manyuda, the Student Council Accountant. What follows is an intense game of "Choice Poker."

The rules for Choice Poker are essentially the same as regular poker, save for a few differences, the most important ones being what makes the game so exciting: during the betting phase, the players are only allowed to place a bet and raise, with the highest bidder earning the right to choose whether a strong hand or weak hand wins. As the accountant and heir of a powerful family, Kaede decides to play with 100 chips, each chip worth ￥10 million. Yumeko, however, is only able to bet on her debt, worth 31 chips.

After losing the initial hand to Yumeko, Kaede realizes that as the chip leader he only needs to beat her bet by one chip in order to be in control of the game. Confident with the ability to read Yumeko's play and decision, Kaede reveals his entire hand to Yumeko before the betting phase begins. Sure enough, Yumeko bets her entire stack of chips, for Kaede to raise her by one chip, declaring that the strong hand wins, winning all of Yumeko's chips.

Despite losing all of her chips, Yumeko asks for Itsuki Sumeragi to serve as a patron, and bid with her money in hopes of continuing the game. Because of Itsuki and Kaede both hope to become the Student Council President, Itsuki decides to help Yumeko. This time, with more money to wager, Yumeko and Kaede engage in a heated battle of bets, until the pool has reached ￥2 billion. Kaede then raises the 100 chips, once again, an amount that Yumeko and Itsuki are unable to match.

Of course, at Hyakkaou money isn't the only thing worth betting, and Yumeko convinces Itsuki to put her life and life worth on the line. Intent on winning the hand, Kaede raises the bet his own life. Using the fact that Yumeko played her hand in the same fashion as the last hand, Kaede decides to call "strong" as the winning hand, putting his life and billions of yen on the line.

After saving Yumeko from being assaulted by Jun and his friends, by challenging them to a game of Russian roulette, Student Council Beautician Midari Ikishima becomes obsessed with Yumeko and her love of gambling. When the change to satiate her interest in Yumeko appears, Midari kidnaps her and Ryota to force her into playing a game.

Midari challenges Yumeko to an ESP matching game, with a game of Russian roulette as the wager. In the game of Russian roulette, both players load as many bullets as they like in the chamber, and put the revolver in a box. The winner of the round chooses a gun at random and has to shoot their opponent. If the persona intentionally misses, however, then the loser gets to shoot them. The winner of the overall game wins ￥1 billion. With Ryota as the dealer, Yumeko is confident that Midari has no way of cheating, and perhaps even her own way to gain an upper hand.

In the first round, Midari wins but chooses Yumeko's gun, which Yumeko claims to have sabotaged before revealing that it's simply unloaded. In the second round, Yumeko manages to win, and point a gun at an eager Midari. Yumeko then reveals that she had chosen her own gun, which she is sure of due to the guns' difference in weight. In the last round, Yumeko and Midari choose to load their guns with two bullets each. Yumeko wins again, and this time, with both guns loaded, there's a real possibility of Yumeko either shooting Midari, as Midari hopes she would or intentionally missing and possibly being shot herself.

Instead, Yumeko reveals that she's aware of how Midari was rigging the game. Unlike other opponents, Midari was actually rigging the game in Yumeko's favor, in hope of being shot and experience pain, what she considers to be life's greatest pleasure. When not accounting for Midari's cheat, both players didn't actually match any cards, ending the game in a draw. Somehow, for the game with the most extreme bets -￥１billion and the risk of bodily injury- it actually had the lowest payout.