"Those Summer Days" is a slice-of-life manga that centers around a group of teenagers navigating the complexities of adolescence during a pivotal summer. The story unfolds in a small coastal town, where the protagonist, a reserved high school student named Haruto, returns after several years away. Haruto reconnects with his childhood friends, including the spirited and outgoing Aoi, the thoughtful and artistic Riku, and the quiet yet observant Sora. Together, they spend their days exploring the town, revisiting old haunts, and confronting unresolved emotions from their past.

The narrative delves into themes of friendship, self-discovery, and the passage of time. Haruto struggles with feelings of guilt over leaving his friends behind, while Aoi grapples with her own insecurities about the future. Riku, who harbors unspoken feelings for Aoi, finds himself caught between loyalty to his friends and his personal desires. Sora, often the voice of reason, provides a grounding presence as the group navigates their shared and individual challenges.

As the summer progresses, the characters confront pivotal moments that force them to reevaluate their relationships and aspirations. A long-forgotten promise made during their childhood resurfaces, becoming a central point of tension. The group embarks on a journey to fulfill this promise, leading to moments of introspection and emotional revelation. The manga balances lighthearted, nostalgic scenes with poignant moments of growth, capturing the bittersweet nature of adolescence and the fleeting beauty of summer.

The coastal setting plays a significant role in the story, with its serene beaches, vibrant festivals, and quiet sunsets serving as a backdrop for the characters' experiences. The manga's pacing allows for a gradual exploration of each character's inner world, revealing their fears, dreams, and vulnerabilities. Through their interactions, the story emphasizes the importance of communication, forgiveness, and cherishing the present.

"Those Summer Days" concludes with a sense of closure, as the characters come to terms with their past and embrace the uncertainties of the future. The final chapters highlight the enduring strength of their bond, leaving readers with a heartfelt reflection on the transformative power of friendship and the memories that define a summer.