Kiba Yuuto (木場 祐斗 Kiba Yūto?) is a second-year student at Kuoh Academy. He is a gentle swordsman and the school's prince whose rank in the Occult Research Club is "Knight", possessing the ability to move at incredibly high speeds. Although he calls himself Issei's friend, he is almost the complete opposite of the latter, sporting good looks, intelligence, and a pretty nice personality. However due to the events in his past, he bears an immense hatred towards the Holy Swords, as well as about everything and everyone associated with them. Much to Issei's dismay, the pairing of him and Kiba has become a hot topic between the girls in the academy.

In the light novels, it is revealed that he was a victim of the Holy Sword Project, where he was the only sole survivor. He became Rias' servant when she saved him from death, and swore to extract his revenge on those who treated him as a test subject and disposed of his friends. As a result, he also harbors a great hatred towards the Holy Sword Excalibur. However thanks to Issei, he can truly let go of his rage. He treats Issei as his best friend, despite the fact that Issei doesn't.

Kiba Sacred Gear, "Sword Birth" (魔剣創造(ソード・バース) Sōdo Bāsu?, lit. "Creation of the Holy Sword"), has the ability to create Demonic Swords like the Holy Eraser (a sword that devours light) or Flame Delete (an ice blade that negates fire attacks). He later gains his Balance Breaker, called "Sword of Betrayer" (双覇の聖魔剣(ソード・オブ・ビトレイヤー) Sōdo obu Bitoreiyā?), which is a fusion between a Demonic Sword and a Holy Sword, during the fight with Freed after he "merged" his Sacred Gear with the spirits of his fallen comrades who were the victims of the Holy Sword Project. The creation of Yuto's Sword of Betrayer became possible after both God and Satan died in the previous war, thus ending the balance between Holy and Demonic powers which allowed the "Holy Demonic Sword" (聖魔剣 Seimaken?) to become possible. Yuto later gains a second Sacred Gear, "Blade Blacksmith" (聖剣創造(ブレード・ブラックスミス) Burēdo Burakkusumisu?, lit. "Creation of the Holy Sword), and a sub-species Balance Breaker called "Glory Drag Trooper" (聖覇の竜騎士団(グローリィ・ドラグ・トルーパー Gurōryi Doragu Torūpā?, lit. "Supreme Holy Dragon Knight Army"), which creates an army of Dragon Knights (竜騎士団 Ryūkishi-dan?), each having Dragon Slayer abilities.

In Volume 11 of the light novels, Yuto took a promotion test along with Issei and Akeno to become middle-class Devils. In Volume 12, Yuto defeats Siegfried (losing one of his arms in the process) after Siegfried's Demon Swords leave him and chose Kiba as their new wielder. At the end of the same volume, Kiba Yuuto is also officially promoted into a Middle-Class Devil.