"Koi no Shoshinsha Mark" centers on the romantic misadventures of Itsuki Akiba, a high school student who struggles with expressing his feelings due to his inexperience in love. Itsuki harbors a crush on his classmate, Natsuki Hoshino, but his attempts to confess his feelings are repeatedly thwarted by his own nervousness and awkwardness. His lack of confidence in romantic matters often leads to comedic and heartfelt situations as he navigates the complexities of young love.

The story explores Itsuki's growth as he learns to communicate his emotions more effectively, often with the help of his friends and classmates. Natsuki, the object of his affection, is portrayed as kind and approachable, but she remains largely unaware of Itsuki's feelings for much of the series. Their interactions are marked by a mix of humor and sincerity, highlighting the challenges of first love and the misunderstandings that often arise between teenagers.

Supporting characters, such as Itsuki's close friends, add depth to the narrative by providing advice, encouragement, and occasional interference in his romantic endeavors. These characters contribute to the series' lighthearted tone while also addressing themes of friendship, self-discovery, and the importance of perseverance in the face of setbacks.

The manga balances comedic moments with genuine emotional development, capturing the awkwardness and vulnerability of adolescence. Itsuki's journey is relatable, as he stumbles through his first experiences with love, learning valuable lessons about courage and honesty along the way. The series maintains a focus on the everyday struggles of high school life, making it an engaging and accessible story for readers interested in slice-of-life romance.