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It was led by Fiamma of the Right as its members sought Godhood and Ultimate Salvation and was responsible for many clashes between both the Roman Orthodox Church and Academy City (as well as Academy City's allies like the Anglican Church and Necessarius). During the clashes however, one of their members was killed and the organization dissolved after Fiamma had managed to get strong enough to reach godhood and betrayed all of his former followers.
God's Right Seat was formed in Europe around the time the Great Calamities were sweeping across Europe. The purpose was to help people talk to the Pope about matters based in the Catholic Church. GRS was also powerful enough for the Papacy to rely on and are considered to be separate from the rest of the Clergy Hierarchies. It is unknown how many members have since then passed through the organization's ranks.
Sometime in the 21st Century, Fiamma of the Right had notices that there was a dissortion of law and order throughout the world that would usher in the Grand Magic Angel Fall to occur and tried to become the La Persona Superiore a Dio (The One Above God ), the highest rank in the Magic Side. Fiamma was willing to do anything to achieve this goal and even manipulated both the Pope and the entire Catholic Church in order to achieve his goals and was willing to go as far as starting World War III.
Academy City Invasion Arc
In the aftermath of the Battle of the Adriatic Sea in which Bishop Biagio Busoni was captured by Necessarius and was sent to prison in the Tower of London along with Lidvia Lorenzetti, the Roman Orthodox Church was put into a state of emergency and so an investigation was launched into Touma Kamijou who had shifted the balance of power in favor of the English Puritan Church, the Science Side, and the Magic Side in favor of the Anglican Church in general. The investigation was ordered by Vento of the Front and during that investigation into Touma, then-current Pope Matthai Reese is summoned to St. Peter's Basilica where she manages to convince him to sign a forum and once he does, Touma is declared to be an enemy of God (and the Catholic Church in general) and Vento is given full authority to go and kill him. She is then sent to Academy City along with Terra of the Left, Acqua of the Back, and supporting invasion force to back her up.
At 6:33 PM, Vento arrives at Academy City where she breaks down Gate 3 and makes it into the city where she attracts the attention of Anti-Skill. Vento then uses her Divine Punishment ability and she affectivly incapacitates all nearby Anti-Skill and Judgment members alike leaving her with no resistance and the security crippled. Her attack then spreads throughout the city's communication lines and thus, no-one is able to report her and she sneaks in without anyone stopping her. Vento then persues to kill three board directors and she then calls Aleister Crowley and mocks him for his weak defenses and vows to destroy Academy City even though Crowley warned her not to underestimate the city. Her arrival and message to Crowely then results in the mobilization of the Hound Dog organization and Kihara Amata to retrieve Last Order from Accelerator. During the invasion, Vento had managed to battle and defeat multiple Hound Dog operatives and she finally made it to Hyouka Kazakiri where she was the source of the Artificial Heaven which had harmed Vento last night. She was confronted by Touma again and they fought once more only to have Vento be defeated. After the fight, she was rescued by Acqua of the Back who escorted her out of Academy City after they were ordered to withdraw. Although Academy City had won, it was left in ruins and much of its defenses were decimated as well.
Document of Constantine Arc
One month after the Invasion of Academy City, tensions began to increase and were high as both Academy City and the Roman Orthodox Church had began to muster their forces in preparation for war. Academy City was left decimated following the attack on September 30th which left the city in ruin and costed Academy City over 8 Trillion Yen in damage. The Roman Church had the balance of power finally shift back in their favor and so, they began planning their next move. Back in Vatican City, Terra of the Left is seen drinking cheep wine in the middle of St Peter's Square replenishing his strength based off of his alignment with the Archangel Raphael. His careless drinking in thre middle of the square had caught the attention of Pope Reese and Acqua of the Back who were talking about Terra once he finally finished his drink. Terra then plans to use th Document of Constantine to cause chaos to the enemies of the Roman Church and Academy City. Terra of the Left had also planned to use civilians as human shields but was immediatly met with opposition by Acqua but he said how it would be a waste if the church didn't use its human resources but went away with it anyway. For much of the sotry arc, Terra of the Left heads towars Avignon, France where he spends most of the time in the Palais des Papes (Palace of the Popes) conducting his plans.
He spends much of his time there meeting with Roman Church Magicians and starts to October Anti-Academy City Riots using the Document of Constantine. Terra then sets up a spell amongst the Vatican-Avignon Key Line to detect intruders nearby the line. Once Academy City Forces had been detected, Terra sends out the Roman Church Magicians under his authority to intercept them as well as Touma Kamijou and Motoharu Tsuchimikado. Touma and Terra then engage in a fight after some small talk until Motoharu arrives and shoots a magical origami figure though Terra uses a balance spell to deflect the attack from him. Eventually however, Avignon comes under attack as Academy City Military Forces begin to arrive in the city which Terra of the Left uses their arrival to escape and allows civilians to be killed in an effort to paint Academy City as nihlistic murderers and flees back to his main base in the Palace of the Popes when Academy City Forces begin bombing the entire city of Avignon and Mikoto Misaka had noticed the French Government not responding to the event.
Eventually however, Touma Kamijou and Terra of the Left confront each other for one last time in their final confrontation and they begin to fight. Terra and Touma are equally matched as Terra is still able to hold his ground despite being weakened and is able to lash out attacks against Touma and can deflect attacks directed at him. Half-way through the fight, Touma asks Terra why he is allowing so many innocent civilians to die at the hands of the battle and why did he even involve them. Terra responds by saying that he desires salvation and he wants to bring it to others and he hopes to use these conflicts in an effort to spread his desires. Touma then fires back at Terra saying that God wouldn't spread salvation through conflicts and that it's not the fault of the Roman Orthodox Church saying how Orsola and Agnese are not twisted and are good people. He then blames Terra himself and accuses him of not knowing what salvation really means. Eventually however, Touma is able to defeat Terra of the Left with one punch to the face and he knocks him out and Touma uses the Imagine Breaker to destroy the Document of Constantine. Terra manages to grab Touma and demands more information about the Imagine Breaker when a bomber flies over and knocks them unconcious due to debris. Terra had survived and he eventually fled back to the Vatican where he met up with Acqua of the Back in St. Peter's Basilica and told him how the mission was still accomplished despite the destruction of the Document fo Constantine since the Russian Achievement Church had allied itself with the Roman Orthodox Church and the Anglican Church had allied with Academy City. Acqua then asks if Terra had used innocent civilians and children for his Execution of the Light spell which Terra says yes and says how Pagans (Non-Catholics) weren't even human. This infurriated Acqua as he smashed one of the pillars of the basilica and cut Terra in half as the last straw to his never-ending attrocities. Terra still has his same look believing that salvation is coming but then, Acqua tells him that his attrocities would not go unnoticed by God and that he would be sent to Hell. He then has a look of disdain and Terra of the Left then finally dies. Following his death, the Pope came in and said to Acqua not to damage to architecture of the basilica
Acqua of the Back Arc
Following the conclusion of the battle in Avignon, Terra of the Left is killed and his corpse is placed into a box and wrapped in cloth by Acqua of the Back after he killed Terra for commiting so many atrocities in the name of both God and the church. After that, Acqua of the Back sends out a message to both the Anglican Church and Academy City challenging them to fight him in an epic dual. The Amakusa Church accepts the challenge but the entire group is completely wipped out by Acqua due to his sheer power and strength. Touma and Itsuwa arrive only to find the Amakusa defeated and Acqua then beats the two of them as well but in a more brutal fashion.
- Fiamma of the Right - The Fourth and final member, Fiamma of the Right (右方のフィアンマ Uhō no Fiamma) is the Leader of God's Right Seat and has been the secret de-facto ruler of the entire Roman Orthodox Church from behind the scenes. He is blessed with the nature of "Likeness of God" and aligns with the Archangel Michael. He posses the ability of the "Holy Right" but is unable to use its true powers and full potential and has searched for a way to acquire the way to have it reach its full potential. To do this, Fiamma goes to England during the civil war and finds Index and takes control of her John's Pen and then heads towards Russia in search of Sasha Kruetzev for being possess by Archangel Gabriel during the Angel Fall Arc of the series. He is the main antagonist of the entire God's Right Seat Arc and is the bigger bad and true main antagonist of the entire Toaru Majutsu no Index series.
- Vento of the Front - First Member seen, Vento of the Front (前方のヴェント Zenpō no Vento) is first appears after the Queen of the Adriatic Sea got destroyed and is the main antagonist of the Academy City Invasion Arc and is the first antagonist of the God's Right Seat Arc to be introduced. She is the only known female member of the group and has been blessed with "God's Flame" and she aligns with the Archangel Uriel. Following her defeat in Academy City, she is eventually betrayed by her former superior Fiamma of the Right who then goes on to start World War III and she ends up going to Russia to help defeat him.
- Terra of the Left - Second Member introduced, Terra of the Left (左方のテッラ Sahō no Terra) is a strange man and is the secondary antagonist of the God's Right Seat Arc appearing in the Document of Constantine Arc as the main antagonist. He is blessed with God's Medicine and is aligned with the Archangel Raphael. His main power is Execution of Light and was responsible for a series of riots against Academy City in October and was stationed in Avignon, France. He appears to have known about Touma's amnesia and is the only one with the closest knowledge of Touma's Imagine Breaker ability. This was confirmed during their confrontation but it was interrupted by an assault on the city by Academy City's Forces. Terra was later on killed at the hands of Acqua of the Back.
- Acqua of the Back - Third Member of the organization, Acqua of the Back (後方のアックア Kōhō no Akkua) is the tertiary antagonist of the God's Right Seat Arc. He waas a mercenary from the United Kingdom and was blessed by the Anglican Church, but he later on changed his religion and converted to the Roman Orthodox Church and became a Roman Catholic. He later on joins God's Right Seat at some point in time and is given the power of "Divine Mother's Mercy" which nullifies his body's limitations and can use his saint powers at 100% maximum. He later on appears during the Document of Constantine Arc where he is forced to kill Terra of the Left for his actions and is the titular main antagonist of the Acqua of the Back Arc where he fights Kaori Kanzaki, another Saint, and is about to win when he is hit by the Saint Destroyer of the Amakusa Christian organization. He eventually redeems himself and faces off against Fiamma in Russia during his betrayal and during World War III and even becomes Touma's ally later on and is part of the unofficial Kamijou Faction.