Two childhood friends, Wakaba and Komaki, have a relationship built on rivalry and resentment. To the outside world, Komaki is a flawless beauty, athletic, intelligent, and kind, but Wakaba knows the truth behind that perfect facade. Komaki is actually cruel, manipulative, and looks down on everyone around her. Determined to prove that her friend is not as special as everyone believes, Wakaba challenges Komaki to a bet. Whoever scores higher on their midterm exams wins. The bet was Wakaba's idea, but it is Komaki who decides to put their dignity on the line.

Wakaba loses. Rather than accept a simple defeat, Komaki declares a new rule for all their future wagers. Each time Wakaba loses, Komaki will claim one of her precious things, specifically all of her first experiences. Her first kiss is the first prize taken. As the bets continue, Komaki systematically claims Wakaba's firsts, from romantic milestones to other significant moments. Wakaba continues to despise her childhood friend, but with each loss and each experience stolen, she begins to discover unexpected new feelings.

The story takes place in a contemporary school setting where the two girls navigate their intense and complicated relationship. The main characters are Wakaba, an ordinary girl who hates losing, and Komaki, a genius with a cruel personality who seems driven to possess everything that makes Wakaba who she is. As the bets escalate and more firsts are taken, the central question becomes what this game truly means to both of them. While Wakaba struggles to understand her own conflicting emotions, Komaki's true motives for wanting Wakaba so badly remain unclear.

The narrative unfolds through a series of competitive bets that push the boundaries of their relationship. What begins as a simple academic challenge evolves into something far more intimate and complicated. Each lost bet leads to a new stolen first, forcing Wakaba to confront the thin line between hatred and attraction. The series explores how a game born from resentment can transform into something neither girl anticipated, as their shared history and forced proximity reveal deeper layers of feeling beneath their competitive surface.