HP to one ability

HP To One abilities are a recurring theme in the Final Fantasy series. They reduce the HP of one or more party members to one, regardless of their current HP. This is sometimes done by simply setting the targets to one HP, at other times by inflicting damage to them equal to their max HP minus one. They are commonly used by Final Bosses and Superbosses. The most famous of these abilities is Heartless Angel, which has become the trademark attack of Sephiroth.

Final Fantasy VIII
Omega Weapon has a similar ability called Megiddo Flame. The ability does not reduce the party to one HP, but deals a guaranteed 9,998 damage to the entire party, and thus the only way to survive is to have 9,999 HP, leaving the party with one HP after the attack hits.