Brush Fire Trophy in Ghost of Yōtei

Kill an enemy by catching grass on fire.

Bronze trophyBase game

Often unlocks during the sensei tale The Bomb Maker in Ishikari Plain, whose fight uses Scorch Bombs. Otherwise:

Buy the Hankyu bow from Ran the Bowyer at Yotei's Shadow Inn in Yotei Grasslands, then talk to her again and upgrade it once for fire arrows.
Craft fire arrows at a camp: next to your horse, hold and pick the ammo option in the bottom right.
Lure an enemy into tall grass, the kind you can hide in, and shoot a fire arrow into it.

The fire has to kill him. Short grass does not burn. Once the map is cleared, ride south along the Sarubetsu River from Matsumae Crossing in Yotei Grasslands: a rope across the river sometimes sets off an ambush from the tall grass.