Gai has black hair and brown/red eyes, and a rather thin build. His right arm is missing below the elbow, and instead replaced by a prosthesis made of the lesser Shiryu. This arm reaches up to Gai's shoulder.
It is shown that he sometimes lacks expressions and can be a bit cold to others. He tends to say that he is alone, believing that the world is against him at all times. This belief makes him desire to kill the entire world, as well as the darkness he perceives is following him. Despite this, he seems to want to help people when they need it, and shows that he genuinely does care about people. He builds some trust with, and desired to fulfill a personal promise made to Seiya Ichijo.
Gai's mother committed suicide near the Ogata household, leaving the Shiryu in the babies arms. Gai was found by Amon Ogata, and taken in to the Ogata family. He studied sword making while living with Amon Ogata, but didn't make many friends, apart from the daughter of Amon, Sayaka.
Once as a child, he tried to run away from the Ogata household, but Sayaka followed after him. This led to her almost being attacked by a wolf, but Gai saved her at the cost of a bite to his arm. As they walked back home, they held hands.
Later on Sayaka tries to convince Gai to have fun with her but he refuses and then he's threatened by Tatsumi, saying that it's his fault(Sayaka tries desperately to protect him). When the cleansing ritual for the Shiryu went wrong and Sayaka got possessed, Gai rushes in to save Tatsumi, losing his arm in the process. He goes mad temporarily and defile his mother's grave
Due to the unique circumstance of his weapon being forged into a cursed prosthetic arm, he can form his entire right arm into the Shiyru's blade, and is shown to be quite capable of using it in combat. He has held his own against powerful and even monstrous opponents, and in most cases, has won these altercations. Gai is not only unique because of the way his weapon is integrated into his body, but Gai is also the only Chrysalis shown to be capable of reverting from Busoma back to Chrysalis.
Gai protects Sayaka from unwanted advances by Tatsumi, which later causes Gai to lose his arm in a ritual gone wrong.
Amon forges the Shiryu into a prosthetic arm for Gai. Gai struggles with the new powers this brings him.
Tatsumi, now a Busoma, and Gai, while in a murderous state of being controlled by the Shiryu, fight. This attracts the attention of the Shoshidai.
Gai and Seiya Ichijo begin to fight, though this gets interrupted numerous times. Gai and Sayaka manage to escape into the forest, and talk for some time before returning to the Ogata household. Seiya offers to take Gai to the Shoshidai, and Gai accepts.
Gai helps Ichijo take down the double-weapon wielding Naoki Miki.
Gai and Ichijo talk for some time, prompting Ichijo to reveal how he came into the possession of the Chakram.
Gai finally arrives safely at the Shoshidai headquarters.
Gai and Ichijo fight with Zsoltgewinn, but as they are about to win the Busoma Grimms interrupts. Gai insists on fighting him, losing control to the murderous rage of the Shiryu. Ichijo's attempts at awakening Gai only cause Gai to become a Busoma, though this leads to Gai stabbing Ichijo. Ichijo then becomes a Busoma, though succeeds in freeing Gai from the control of the Shiryu.
Episode 12- season 2 Edit
Gai gets stabbed by Sayaka with the blade he previously made for her to protect herself. The pain he felt as a result gave him the power to overcome the control of the Shiryu. Now back in control of his own body he fights Shin Matoba who has the other, superior, version of the Shiryu. Just when Shin seems to win the battle he admits to Gai that he doesn't think he can stay in control and decides to allow Gai to kill him. As a result the other Shiryu also gets absorbed into Gai and turns Gai into what Grimms calls "the God of the Busomas". But instead of this "God" killing all humans as Grimms had planned all allong we get to see how Gai, Amon an
Amon Ogata is Gai's adoptive father, but Gai doesn't seem emotionally attached to his adoptive father at all, though he says "he is grateful for what his master has done for him."
Sayaka Ogata is Gai's adoptive sister, though Gai tends to brush her aside often. However, he is also shown helping her and taking injuries in her stead, proving he does genuinely care for her. Though not quite shown to be reciprocated by him, Sayaka is strongly suggested to be in love with Gai despite his cold nature.
Seiya Ichijo takes on a mentor like role for Gai in the brief amount of time that they spend together.