"My Clueless First Friend" centers on the unlikely friendship between Nishimura Taiyou, a cheerful and socially oblivious boy, and Hikari Takada, a quiet and reserved girl who is often misunderstood by her classmates. Taiyou transfers to Hikari's school and, unlike others, does not perceive her as gloomy or intimidating. Instead, he sees her as a fascinating and kind person, earning him the nickname "Grim Reaper" due to his association with her. Despite this, Taiyou remains unfazed and continues to approach Hikari with genuine curiosity and warmth.

The story unfolds through their daily interactions, highlighting Taiyou's unwavering positivity and Hikari's gradual opening up to his friendship. Taiyou's cluelessness about social norms and his straightforward nature often lead to humorous and heartwarming situations, as he unintentionally breaks down the barriers Hikari has built around herself. Their relationship evolves as they navigate school life, with Taiyou's presence helping Hikari gain confidence and form connections with other classmates who begin to see her in a new light.

The manga explores themes of friendship, acceptance, and the impact of kindness, portraying how Taiyou's innocence and sincerity challenge the preconceived notions others have about Hikari. Secondary characters, such as classmates and teachers, add depth to the narrative, showcasing varying perspectives on the pair's friendship and the broader dynamics of their school environment. The story balances lighthearted moments with subtle emotional depth, emphasizing the transformative power of understanding and compassion.