Masamune Makabe, a once-overweight boy who was cruelly rejected by a wealthy girl named Aki Adagaki during his childhood, undergoes a dramatic transformation. Determined to exact revenge, Masamune reinvents himself into a handsome and confident high school student. His plan is to make Aki fall in love with him and then reject her, mirroring the humiliation he endured. Upon transferring to Aki’s school, Masamune quickly gains her attention, but his scheme becomes complicated as he navigates her unpredictable personality and the dynamics of their shared social circle.

Aki Adagaki, known as the "Brutal Princess" for her sharp tongue and disdain for men, initially appears to be the perfect target for Masamune’s revenge. However, her behavior and interactions with Masamune reveal layers of vulnerability and insecurity, complicating his feelings. As Masamune grows closer to Aki, he begins to question whether his desire for revenge is still justified, especially as he uncovers her own struggles and the reasons behind her past actions.

The story introduces several supporting characters who add depth to the narrative. Yoshino Koiwai, Aki’s maid and childhood friend, plays a pivotal role as she manipulates events to protect Aki while also harboring her own secrets. Neko Fujinomiya, a wealthy and eccentric girl, becomes a rival for Masamune’s affections, further complicating his plans. Other characters, such as Masamune’s childhood friend Tae Futaba and the cheerful but clumsy Kojuurou Shuri, contribute to the romantic and comedic tensions within the series.

In "Masamune-kun's Revenge R," the second season, the narrative delves deeper into the unresolved conflicts and emotional entanglements from the first season. Masamune’s revenge plot reaches a critical juncture as his feelings for Aki become increasingly conflicted. The introduction of a new character, Gasou Urushima, who claims to be the real Masamune from Aki’s past, adds a layer of mystery and tension. This development forces Masamune to confront his identity and the authenticity of his connection to Aki, while Aki herself grapples with her feelings and the truth about her childhood.

The series balances comedic moments with emotional drama, exploring themes of self-worth, forgiveness, and the complexities of human relationships. As the characters navigate misunderstandings, rivalries, and personal growth, the story builds toward a resolution that challenges their perceptions of love and revenge. The interplay between humor and heartfelt moments creates a dynamic narrative that keeps viewers engaged while addressing the central question of whether Masamune’s quest for vengeance will ultimately lead to happiness or regret.