Balance Breaker

The Balance Breaker, also known as the Forbidden Move, is the evolved form of Sacred Gears and Longinus.

Summary
Azazel claims that the Balance Breaker is a "bug" created in the system by the original God which can upset the balance of the world and thus given the name Balance Breaker. The Balance Breaker is initially considered a forbidden power by all the factions. It is called the ultimate state of activation of a Sacred Gear.

Balance Breaker is initially triggered by high emotions combined with a change in the heart or spirit of the wielder. It is also when the user is faced against odds, like when Issei had to face against both Bikou and Kuroka in volume 5.

Abilities
The Balance Breaker is the most powerful manifestation of all Sacred Gears in which the possessor's feelings trigger this evolution. Once reached, the Balance Breaker can be entered again far more easily than the first time. With proper training, it can be maintained for longer periods of time, as with the case with Vali. While initially Issei could only maintain it for small periods of time, undergoing intense training helped him improve this time. When introduced, Vali could maintain his Balance Breaker for a month. The forms of each Balance Breaker differ according to the user.

Sub-species Balance Breakers
Balance Breakers can also have a sub-species, the sub-species Balance Breaker creates a diferrent form of than the actual ones and are usually more powerful than the actual ones. The method to attain a sub-species Balance Breaker is currently unknown but seems to involve the user's personality.

Known Balance Breakers

 * Issei's Boosted Gear's Balance Breaker is the Scale Mail, a Red Dragon Armor that covers Issei's body.
 * Yuuto's Sword Birth's Balance Breaker is a sub-species, the Sword of Betrayer, a Holy Demonic Sword.
 * Yuuto's Blade Blacksmith's Balance Breaker is a sub-species of the original Balance Breaker, Glory Drag Trooper, where he creates Holy Sword wielding Dragon knights instead of regular knights.
 * Vali's Divine Dividing's Balance Breaker is also the Scale Mail; however, a White Dragon Armor covers Vali's body instead of the Red Armor used by Issei.
 * The Hero Faction member that has the Night Reflection's Balance Breaker is Night Reflection Death Cross, which creates a shadow armor. This could be a sub-species because the user said he wanted defence and an armor like Issei's Scale Mail after his defeate in voulme 7. Death Cross's abillities is that the user becomes like a shadow, making physical attacks pass right through him, although the user still feels thing like heat and cold.
 * Cao Cao's True Longinus' Balance Breaker is a sub-species, the Polar Night Longinus Chakra Valdine, which creates a ring of light and seven orbs around him, each giving him a special ability, and the True Longinus is still a spear which he can use.
 * Jeanne's Blade Blacksmith's Balance Breaker is a sub-species, Stake Victim Dragon, which creates a dragon made of Holy Swords.
 * Siegfried's Twice Critical's Balance Breaker is a sub-species, Chaos Edge Asura Ravage, which creates four Dragon Arms, each doubles his power for a total of sixteen times his original strength.
 * Heracles' Variant Detonation's Balance Breaker is the Detonation Mighty Comet, which creates missiles that grants Heracles the power to make things out of his reach explode by firing the said missiles.
 * Sairaorg's Regulus Nemea's Balance Breaker is a sub-species that creates a Golden Lion Armor that gives him the power of the Regulus Nemea to split the earth as a battle axe to his fists and it protecs him from attacks.
 * Georg's Dimension Lost's Balance Breaker is the Dimension Create, which creates a stronger barrier than the one the Dimension Lost and can create numerous barrier-related devices.
 * Leonardo's Annihilation Maker's Balance Breaker is Jabberwocky and Bandersnatch, a sub-species, which creates thirteen gigantic monsters (one Jabberwocky and twelve Bandersnatches). Both monsters have the abillity to create smaller copies of themselves, while the Jabberwocky has the abillity to regenerate damaged parts of its body.

Trivia

 * Currently, the number of sub-species Balance Breakers outnumber the actual ones.
 * Some fans consider Issei's Illegal Move Trident to be a sub-species of his Scale Mail.