blood, sweat and tears; sweat of blood
Idiomatic expression for extreme effort and suffering; literally 'sweat of blood'. Used to describe grueling hardship or toil.
彼は血の汗を流して働いた。
He worked with blood, sweat and tears.
成功するまで血の汗をかく覚悟だ。
I'm prepared to go through hell until I succeed.
Compound of 血 (blood) + の (possessive particle) + 汗 (sweat), literally 'sweat of blood'. The figurative meaning is shared with similar expressions in other languages.