"Deep Voice" centers on a young man named Haruto, who possesses a unique and powerful singing voice that captivates everyone who hears it. Haruto, however, struggles with self-doubt and a lack of confidence, stemming from a traumatic childhood incident where his voice was ridiculed. Despite this, he dreams of becoming a professional singer. The story unfolds as Haruto is discovered by a talent scout from a prestigious music academy, where he is offered a chance to hone his skills and pursue his passion.

At the academy, Haruto encounters a diverse group of talented individuals, each with their own struggles and aspirations. Among them is Aoi, a prodigious pianist with a perfectionist streak, and Riku, a charismatic guitarist who hides his insecurities behind a carefree demeanor. The trio forms a bond as they navigate the competitive and often cutthroat world of the music industry. Haruto's journey is marked by intense training, rivalries, and personal growth as he learns to overcome his fears and embrace his talent.

The narrative explores themes of perseverance, self-discovery, and the transformative power of music. Haruto's relationships with his peers and mentors play a crucial role in his development, as they challenge and support him in equal measure. The series delves into the pressures of fame and the sacrifices required to achieve one's dreams, highlighting the emotional and psychological toll it can take on individuals.

As Haruto progresses, he faces numerous obstacles, including a rival singer who seeks to undermine him and internal struggles with his identity and worth. The climax of the series sees Haruto performing in a high-stakes competition, where he must confront his deepest fears and prove his worth as an artist. The resolution of the story emphasizes the importance of authenticity and staying true to oneself, as Haruto's journey inspires those around him to pursue their own dreams with renewed determination.