Kōsei Arima is a fictional character from the popular anime and manga series Your Lie in April. He is a talented pianist who struggles with his emotions and the pressure of performance after the death of his mother. His journey revolves around rediscovering his passion for music through his interactions with other characters. In the series, Kōsei meets Kaori Miyazono, a free-spirited violinist who inspires him to embrace his feelings and overcome his past. Their relationship plays a crucial role in Kōsei's growth as both a musician and an individual, highlighting themes of love, loss, and the healing power of music.