The plot is almost the same with the canon so I will write the summary of the story that shows the difference. Read the background on the character that I alter first before read the summary. Please forgive my grammar mistakes and enjoy my first fanfic.
Name: Toujou Koneko
Gender: Female
Evil Piece: Rook
Pairing: Kiba Yuuta
Ability: Senjustu and Youjutsu (not using them due to trauma)
History: Koneko is a Nekomata who is part of a rare species among a kind, called was sentenced to death by the Devils after her sister killed her master and became a Stray Devil. However, Sirzechs Lucifer protected her and left her under his sister, Rias' care. Due to the trauma she experienced, she fell into a deep depression and rarely show emotion. She will show some emotion arond Kiba and blushes when Kiba pets her head (Kiba always assume Koneko is having fever when she blushes). Due to Kiba's kind and protective nature, Koneko grow affection towards Kiba and often be around with Kiba. She often fights with Gasper to sit on Kiba's lap (later include Artoria). She marks Kiba's as her personal sit and she sits on his lap when she found a chance.
Name: Gasper Vladi
Gender: Female
Evil Piece: Bishop (Mutation)
Pairing: Kiba Yuuta
Sacred Gear: Forbidden Balor View
History: Gasper is a Dhamphir, half-vampire. She grew up in isolation and abused due to her sacred gear and being half breed. Her best friend was Valerie Tepes and they would often play together. Gasper has cross-dressing habit because of Valerie forcing Gasper to dress up as a boy. One day, she escaped from the castle with the help of Valerie but was shortly killed by vampire hunters. She was then reincarnated by Rias Gremory as one of her servant. She likes to be together with Kiba as she feel being protected. She often fights with Koneko to sit on Kiba's lap (later include Artoria).
Name: Kiba Yuuta
Gender: Male
Evil Piece: Knight
Pairing: Toujou Koneko, Gasper Vladi, Artoria(OC)
Sacred Gear: Sword Birth (Former)
Gradation Air (Evolved from Sword Birth)
Equipment: Excalibur
History: Kiba was originally a orphan and chosen to be a part of The Holy Sword Project. He along with his friends were eliminated after The Holy Sword Project ended. After successfully escaping the facility with the help of his friends, he finally succumbed to the poison he inhaled. He was found by Rias who revived him as her servant. He was trained under Okita Souji, Sirzechs Lucifer's Knight. Kiba has obsession with swords and able to feel the emotions of the swords. He is a very polite and kind to people around him. He is also protective and care deeply for his comrades. He cannot make himself to hate Excalibur due to his love towards swords. Sometime he will dream of a world filled with may swords. He tried to create the swords he saw in his dream using Sword Birth but failed. After he evolved Sword Birth into Gradation Air, he can create the married twin sword, Kanshou and Bakuya.
Name: Artoria(OC)
Gender: Female
Appearance: Look like Saber from Fate/Stay Night but in child form
Pairing: Kiba Yuuta
History: Artoria was actually the conscience of the Excalibur and she can take the form of a she was broken into seven fragments, she lost conscious and went into deep slumber. Those fragments were reforged into seven new swords called Excalibur Rapidly, Transparency, Nightmare, Mimic, Destruction, Blessing and Ruler. The seven new swords were kept by the Church with Eastern Orthodox Church having three of them while Catholic Church and Protestant Church had two each. All three from Eastern Orthodox Church were stolen by Kokabiel while one from each remaining Church were stolen by his followers. After Kokabiel was defeated, all seven fragments were kept by Sirzechs Lucifer in order to return them to Michael during the meeting between three factions. During the attack of the Khaos Brigade, all the seven fragments once again combine to form the complete Excalibur and choose Kiba as her new wielder. She will only take the form of the sword when fighting and take the form of child most of the time. She always show affection to Kiba and likes Kiba to praise her. She will fight with Gasper and Koneko to sit on Kiba's lap.
Gradation Air
Gradation Air is evolved from Kiba's Sword Birth with the help of his friends. Gradation Air allows Kiba to create any kind of swords as long as he can imagine it. He cannot create the swords that appear in his dream except a pair of blades called Kanshou and Bakuya.
His Balance Breaker allow him to transfer the people around him to a world filled with swords. In that world, it is filled with swords that he created, the swords in his dream and the sword he saw. He can use all the sword in that world and Excalibur at their full potential. He can maintain his Balance Breaker as long as he is conscious.
To activate his Balance Breaker, Kiba has to chant:
I am the bone of my sword
My body as the core is made out of steel
I have been through many battles
Never once surrender, nor once retreat
Have filled the world with many swords
And become the ruler of that world
Balance Breaker, Unlimited Blade Work
Summary of the Story (Kokabiel Arc and Peace Arc)
Kiba had always wonder on how he react when he encounter Excalibur. Would he be angry as that sword reminded him of his death friends or joy for able to encounter the strongest sword. Instead of both feelings, he felt sympathy the moment he laid an eye on both Excalibur Destruction and Mimic that showed by Xenovia and Irina. Although it was faint, he could feel that the swords were showing both sorrow and sadness. He abandoned the idea of destroying the Excalibur after Xenovia told him the mastermind of The Holy Sword Project, Valper Galilie was working for Kokabiel and was now in Kuoh Town. Kiba tried to leave to find Valper but he dismiss it after Koneko stopped him and told him that she would be sad if he was gone.
At that night, Kokabiel showed up in Kuoh Academy. Gremory group gathered to confront Kokabiel while Sitri group set barrier around the school. Gremory group went into the school field and saw seven Excalibur floating while releasing extreme lights. They also saw both injured Xenovia and Irina lying on the floor unconscious. Valper declared that he was going to make seven Excalibur back into one. Before Gremory group could do anything, divine light spread throughout the school field. When the bright lights were gone, there was one holy sword at the center of field giving out blue-white aura. Valper told the Gremory group that the town would collapse within twenty minutes due to the spell on the ground was completed by the light created by the Excalibur and defeating Kokabiel was the only way to dispel it. Kiba told Valper that he was the survivor of The Holy Sword Project and he declared that he would kill Valper as the revenge for his friends. Instead of feeling afraid, Valper told them the truth about the The Holy Sword Project. The Gremory group and even both Xenovia and Irina who just gained conscious were shocked to know that Valper and his people killed the children after they extracted the element to wield Holy sword from the children. When Xenovia told Valper that she would kill him in the name of God, Valper laughed before he told them that the God was dead. All people except Freed and Kokabiel were shocked and could not believe what Valper said. Kokabiel supported Valper's words by telling them that the God was dead along with the Maou during the Great War. Xenovia could not accept the truth while Asia and Irina fainted.
Valper then threw the orb that made from the element that extracted from the children as he did not need it anymore. It rolled on the ground and went to Kiba's foot. Kiba picked it up with a sad expression before it started to give out shallow lights. The lights started to spread and cover the whole school field. Lights came out from the ground and formed the shapes of boys and girls who were surrounding Kiba. They looked at Kiba with dear and sad expression. Kiba was shocked and happy for able to see his friend again although they were spirits. They gave supporting words to Kiba before yhey turned into a big light that fell down on Kiba. Kiba closed his eye and he recalled the dream that he sometime dreamt of. In that dream, he was in a world that filled with many swords. He once tried to create one of those swords he saw but failed. When he saw a pair of swords which he somehow knew the names were Kanshou and Bakuya, he felt that those swords were flawless and he wanted to create them no matter how impossible it was. Kiba's desire and the supports from his friends enable his Sword Birth to evolve. Kiba named his newly evolved Sacred Gear as Gradation Air before he created Kanshou and Bakuya on his hands.
Kokabiel was impressed that Kiba could still fight after he heard a shocking news. Kokabiel then ordered Freed to use the Excalibur before he summoned five Cerberus. The Gremory group and Xenovia snapped out from their confusions and determined to win against Kokabiel. Xenovia summoned her Durandal to aid Kiba against Freed but decline by Kiba. Kiba told her that he would handle both Freed and Valper while she should help his friend against Cerberus. Freed ran towards Kiba with speed granted from Excalibur but his attack was blocked by Kiba using both Kanshou and Bakuya. Both of them exchanged blows with each other and Kiba started to overwhelm Freed. Freed began to panic and tried to use the ability granted by Excalibur to defeat Kiba but Kiba counter all his attack. Excalibur began to crack while both Kanshou and Bakuya remained unscratch. Kiba told Freed that the Excalibur on his hand was only a broken Excalibur that merged together by force before Kiba shattered the Excalibur into pieces. Freed was shocked and Kiba gave him a final blow which caused him to lost conscious. After that, Kiba created three different swords which were Holy, Demonic and Holy-Demonic swords. The sword levitated within the air before Kiba fired them towards Valper and killed him. Then, Kiba joined his comrades to fight against Cerberus and later Kokabiel.
However, they could not defeat Kokabiel as he was more experience and powerful than them. Before Kokabiel could give them finishing blow, Vali, the Vanishing Dragon interfered and defeated Kokabiel. He then retrived both Kokabiel and Freed to Grigoji base. After the reinforcements arrived, they restored the school and retrieved the Excalibur fragments. Sirzechs planned to return the Excalibur fragments to Michael during the meeting between the three factions in Kuoh Academy. Irina returned to headquarters of the Church although she learned the truth of the God while Xenovia was reincarnated as Rias' Knight. Before Irina left, she told Xenovia that they were still friends although Xenovia became a devil. A few days later, the meeting between three faction were held in Kuoh Academy. Gasper, who was released from the sealed room and Koneko were left in the Occult Research Club's clubroom while the other members of Occult Research Club and Student Council went for the meeting between the three factions.
During the meeting, all people except the leaders, Vali, Issei, Rias, Xenovia and Kiba were froze. It was revealed that they were under the attack of Khaos Brigade and they used Gasper's Sacred Gear in their attack. After Issei and Rias rescued Gasper and Koneko, Vali betrayed Azazel who just defeated Katerea using his artificial Sacred Gear. Vali revealed his true name, Vali Lucifer and his goal to fight with strong people. Suddenly, a man appeared and introduced himself as Arthur Pendragon, the descendant of King Arthur. He revealed himself as the comrade of Vali in Khaos Brigade. He told them that he wanted to retrieve the Excalibur that once belongs to his ancestor. When Michael did not agree to it, Arthur said that he would take it back by force.
Kiba challenged Arthur to a one-to-one duel while Issei fought with Vali after Vali angered him. Kiba created Kanshou and Bakuya to fight with Arthur but they shattered after being hit by Arthur's Caliburn. Before Arthur could give Kiba a final blow, the fragments of Excalibur in the meeting room glowed and combined to form a complete Excalibur. The Excalibur flew towards Kiba and chosen him as the new weider. Kiba used the Excalibur to block Arthur's Caliburn. Both of them exchanged blow using their own Holy swords. Before they could finished their duel, a figure appeared beside Vali. The figure was later identified as Bikou and he came to ask Vali and Arthur to return. Before the three of them sink into the black darkness that spread over the ground, Arthur said he no longer wanted to retrieve the Excalibur as the Excalibur had already chosen Kiba as the new wielder and declared Kiba as his rival. After that, the meeting continued and peace was achieved between the three faction.
After a few days later, Azazel showed up in the clubroom and revealed himself as the advisor of Occult Research Club. He would help to train the devils in the school. Rias, Akeno, Asia and Xenovia were staying in Issei's house while Koneko and Gasper were staying in Kiba's apartment along with Excalibur which took a child form and named herself Artoria. The members of Occult Research Club planned to train in the Underworld before they participate in Youth Devils Gathering.