Your lie in April.

She passes away during Kousei's final piano competition in the last episode.Kaori Miyazono dies at age 15 in Your Lie in April following a risky,ultimately unsuccessful spinal surgery aimed at treating her undisclosed,progressive illness (often linked to Friedreich's ataxia in fan theories).Her death occurs simultaneously with Kousei's final performance,appearing as a hallucination/spirit fading away.