You Dropped This Trophy in Ghost of Yōtei

1. Buy Onryō > Attacks > Disarm Counter at an Altar of Reflection.
2. When an enemy charges an attack that glows yellow, hold and let go to disarm him.
3. Press R2 to pick up his weapon, then to throw it back at him.

The throw has to kill, so wound him a little first. Use the Disarm Counter, not Onryō's Strike: the strike often kills outright. Once the map is cleared, the group at the main entrance of Benten Port in Oshima Coast is always there.