You need to have another battler on the field. A condition where all player characters are dead triggers a defeat event. Would it be possible to modify your tutorial to have at least one living battler before killing the other?
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Unfortunately, what I have in mind is that the player is in a 1v2 battle with one player and two enemies. Unfortunately, adding another battler would compromise that! If it can't be done with the dead condition, could it be possible to make the event occur when the character's HP drops too low instead?