bloodshed; rain of blood
Figurative expression for violent bloodshed, often in dramatic or literary contexts. The literal meaning 'rain of blood' is also possible but less common.
戦場はまさに血の雨が降るような惨状だった。
The battlefield was a horrific scene, as if a rain of blood were falling.
Compound of 血 (chi, 'blood') + の (no, possessive particle) + 雨 (ame, 'rain'), literally 'rain of blood'. The figurative sense of 'bloodshed' is a natural extension.