noun, noun or participle which takes 'suru', transitive verb
writing in blood
Refers to the act of writing with blood, often in a dramatic or historical context. Can be used as a noun or as a suru verb.
彼は血書で遺言を残した。
He left a will written in blood.
Compound of 血 (blood) and 書 (writing). The reading けっしょ is the on'yomi of both characters.