"Those Not-So-Sweet Boys" centers on Yuki Hirakawa, a high school girl who moves to a new town and becomes entangled with a group of delinquent boys known for their intimidating reputations. The story begins with Yuki encountering the trio—Riku, Kyō, and Tōya—after a misunderstanding leads to her being mistaken for a thief. Despite their rough exteriors, the boys gradually reveal more complex personalities and backstories, challenging Yuki’s initial assumptions about them.

Riku, the de facto leader, is fiercely protective of his friends and harbors a sense of responsibility for their well-being. Kyō, the most volatile of the group, struggles with anger management but shows a softer side in his interactions with Yuki. Tōya, the quiet and observant one, often acts as the voice of reason, balancing the group’s dynamics. As Yuki spends more time with them, she uncovers the reasons behind their delinquent behavior, including family issues, societal judgment, and personal insecurities.

The narrative explores themes of friendship, trust, and personal growth as Yuki helps the boys navigate their struggles while also confronting her own challenges. Her presence becomes a catalyst for change, encouraging the trio to reflect on their actions and aspirations. The story balances lighthearted moments with emotional depth, depicting the evolving relationships between Yuki and the boys as they support each other through misunderstandings, conflicts, and moments of vulnerability.

Romantic undertones develop between Yuki and Riku, adding a layer of tension and complexity to their interactions. However, the focus remains on the group’s collective journey rather than solely on romance. The manga delves into the importance of second chances and the impact of genuine connections, portraying how Yuki and the boys influence each other’s lives in meaningful ways. Through its exploration of character dynamics and personal struggles, "Those Not-So-Sweet Boys" offers a nuanced portrayal of redemption and the power of human connection.