As far as I know, the only way to defend against that attack is by preemptively using a Hero, Holy War, or Invincible Moon (one of Rinoa's limit breaks), making at least one character on your team invincible.
As for the Lv5 Death thing, I usually have 100 Deaths on each of my party members, and if they have St.Atk-J, I junction it to their status attack. You'd be surprised how many bosses are vulnerable to Death.