Kosei Arima was a genius pianist intil his mother's sudden death took away his ability to play.

Each day was dull for Kosei. But, then he meets one violinist by the name of Kaori Miyazono. This care-free, independent, and sometimes short-tempered girl had an eccentric playing style that inmediately fascinated Kosei. His once monotonous life was about to change forever.

[Source: official English website]

OVA focusing on Kousei, Emi, and Takeshi when they were younger, showing their troubles during their competitions and the beginning of their rivalry.

[Source: Shigatsu wa Kimi no Uso wiki]