Sacred Gear

Sacred Gears (神器（セイクリッド・ギア） Seikuriddo Gia), also known as God's Artifacts, are powerful equipment bestowed to humans by the original God. They are one of the main focus of the High School DxD series.

Summary
It is explained that the original God created the Sacred Gears as part of His system to enact miracles on Earth. It is mentioned that those humans with Sacred Gears have become very powerful and influential, but no example has been given. There can be more than one Sacred Gear of the same type such as Twice Critical and Blade Blacksmith. The only exceptions appear to be the Longinus, which are all unique. If the Sacred Gear is removed from their owner, the possessor will die.

Only humans or human hybrids are born with Sacred Gears. Angels and Devils can obtain them by resurrecting a human or human hybrid as one of their own. The Fallen Angels have devised a ceremony to extract and possess a Sacred Gear from the original user.

It is possible for an individual to own more than one Sacred Gear. As to why Angels and Devils are never born with them, yet keep them when transformed from humans, is another mystery. Presumably because God never foresaw the new systems of reborn Devils and Angels which arose after His death.

Abilities
Sacred Gears can have a variety of effects, such as Asia's Twilight Healing granting near-intstantaneous healing and Siegfried's Twice Critical doubling the power of the user. Yuto's Sword Birth, for example, can create swords imbued with different attributes, examples include creating a sword that absorbs holy energy, a sword that devours flame, and a sword that absorbs wind.

Balance Breaker
Sacred Gears have an ultimate state of activation called the Balance Breaker, which is the most powerful manifestation of the Sacred Gear. Once reached, the Balance Breaker can be entered again far more easily than the first time. Reaching the Balance Breaker can be triggered by the feelings of its possessor. Balance Breaker is said to be have been never intended, and that it was a flaw in the system created by God.

Juggernaut Drive
Juggernaut Drive is a special ability exclusive to the Longinus Boosted Gear and Divine Dividing, and are considered to be forbidden moves. The Juggernaut Drive temporarily removes the seal placed on the Heavenly Dragons, but the users will lose their sanity while their lives are devoured by the power.

For other Sacred Gears that have creatures sealed inside (such as the Regulus Nemea), their Juggernaut Drive goes under a different name called "Breakdown the Beast" (覇獣（ブレイクダウン・ザ・ビースト） Bureikudaun za Bīsuto).

Chaos Break and Chaos Drive
A special doping for Sacred Gear made from the blood of the original Satans, created by the Hero Faction with the help of the Old Maou Faction. The doping, called Chaos Break, allows the Sacred Gear to undergo Chaos Drive, in which the Sacred Gear fuses with the user while transforming the user into a monstrous form. The names are taken from the Balance Breaker and Juggernaut Drive. In Volume 12, it is stated that after the first use, each subsequent Chaos Break will permanently reduce the user's lifespan.

Artificial Sacred Gears
It is possible for artificial Sacred Gears to be created. Azazel, the leader of the Fallen Angels and Grigori, has conducted countless research on Sacred Gears. He eventually manages to create his own Sacred Gear, the Down Fall Dragon Spear, using the jewel of Fafnir, one of the five Dragon Kings. Artificial Sacred Gears, however, are inferior to the real ones.

Sub-Species
Sub-Species are Sacred Gears that have taken on a unique characteristic because of the thoughts and feelings of the wielder. They are more powerful than the normal form of the same Sacred Gear, and will sometimes gain a new ability as well. Sometimes, both the Sacred Gear in its normal state, as well as the Balance Breaker will be a Sub-Species, Seigfried's for example, but other times, only the Balance Breaker will be a Sub-Species, such as Yuto's Blade Blacksmith. Even Longinus can gain a Sub-Species Balance Breaker like Sousou's True Longinius's Polar Night Longinus Chakra Valdine and Sairaorg's Regulus Nemea Regulus Rey Leather Rex.

Longinus
Aside from the normal Sacred Gears, there are the Longinus. Longinus are top-tier Sacred Gears, each having multiple abilities compared to a normal Sacred Gear which only has one. There are 13 Longinus in total. However, Azazel has stated that there is the potential for more Sacred Gear to eventually evolve into Longinus, under the right conditions.