This is the 9665th most frequent Japanese word.
自首
"Surrender to authorities" or "turn oneself in."
In this sentence, 自首 is used to mean voluntarily confessing to one's wrongdoing.
彼は罪を犯したが、すぐに自首した。
He committed a crime but surrendered himself immediately.
Here, 自首 refers to the act of voluntarily surrendering and confessing one’s crimes with bravery.
自首するのは勇気が必要です。
Turning oneself in requires courage.
In this context, 自首 describes the act of voluntarily surrendering oneself supported by an institutional system.