Lightblade

The hardlight blade is a Forerunner melee weapon composed entirely of hard light. It is affixed to the arms of the Promethean Knights of Requiem.

Gameplay
The blade performs similar to an Energy Sword in that it can strip away energy shields and cut through armor with relative ease. The blade is unwieldable to players as the weapon disintegrates along with the rest of the body immediately after the Knights are defeated. However, it is usable by players when they are assassinating a Knight, whereupon the player tears the blade-arm off the Promethian and uses it to stab its former owner in the chest for the kill.

Trivia

 * There are 7 types of Hardlight Blades in the games, a unique type per Promethean Knight class (Basic, Lancer, Battlewagon, Commander, Marshal, and Strategos)
 * The 7th type functions differently from the others, as it starts as a closed up disc shape, and then hardlight extends from two ends. It is used by Warden Eternal.

List of appearances

 * Halo 4
 * Terminals
 * Spartan Ops
 * Halo: Escalation
 * Halo 5: Guardians