That . . . depends. If Nii never finds out about it, he does nothing. If Nii finds out but Koumyou makes sad faces at him, he . . . might not do anything. Or he'll just be more sneaky about it. If Nii finds out and Koumyou doesn't get to him first, he will kill the person who killed Koumyou.

If it happened during a game (ie all of Ruby died or Koumyou sacrificed himself), it would be different and really depend on how things went down.

If someone did kill Koumyou, would Acedia join Nii for a spot of murder?