Foe Requiem is a series of songs in Final Fantasy XI. They effect one single enemy. There are 6 versions of the song, I through VI, and all of them have the effect of a very light damage over time, similar to a poison. Foe Requiem is highly difficult to resist, and can only be removed by Erase. Its only downfall is that it is not very powerful.
The duration can be increased and a requiems resistability can be decreased if a character has equipped a Flute, Siren's Flute, or Shofar when singing the song.