Kurogane Family[]
Ikki Kurogane[]
Ikki is Ouma's younger brother. Ouma though doesn't care much about Ikki, believing that Ikki isn't truly strong as he merely uses "dirty tricks" to win. Ouma only cares about him as a possible obstacle for Stella, fearing he might slow Stella's progress, even once trying to kill him. Ouma, however, did later admit that he may have been a little wrong about Ikki and despite grudgingly recognize his strength. He also seems to still care a little about him when he let Ikki sleep in his room when Stella and Sara chase after him. Ouma assists his little brother in preparing for his fight against Stella stating that: It is my duty as your older brother to beat the dullness out of you before you are killed. Ikki on the other hand, somewhat admired Ouma in his childhood, for his dedication and ability to carry the wishes of everyone on his back. In the present, however, Ikki has a more neutral look at Ouma, though still believes him to be strong.
Itsuki Kurogane[]
Itsuki is Ouma's father. Itsuki and Ouma seem to have a rather neutral relationship, as Ouma left home at a young age. Itsuki though shows some trust in Ouma, having asked him to join Akatsuki, and despite having left home, Ouma obeyed his father's request, indicating a level of loyalty to him.
Shizuku Kurogane[]
Ouma's younger sister. Shizuku and Ouma also have a rather neutral relationship, though Shizuku still recognizes his strength.
Hagun Academy[]
Stella Vermillion[]
Ouma holds Stella in high regard, believing that she is the opponent he has been searching for. She, in fact, his main reason for joining Akatsuki Academy and participating in the current Seven Stars Sword Art Festival since she held the highest magic power in the world and desired to fight her to cease the shaking caused by facing off against the Tyrant. Though Ouma was disappointed after seeing that her ultimate technique was overpowered by his to the point of blaming it on her following the path of his little brother and even attempted to force him to abandon the Seven Stars Sword Art Festival. Stella recognizes Ouma and his strength, facing him being the main reason for her training with Nene. Stella, however, isn't as obsessed with Ouma as he is of her.
Tohka Todo[]
Ouma and Tohka faced each other during Akatsuki's assault on Hagun Academy. Tohka was shocked by Ouma's utter strength, with Ouma being unimpressed by Tohka but he took her seriously after she was able to injure him using her Takemikazuchi.
Akatsuki Academy[]
Reisen Hiraga[]
Reisen is the leader of Akatsuki, with Ouma following his orders. Ouma, however, is annoyed by his antics, and constant talking. Ouma has a mostly neutral relationship with the other Akatsuki members, not caring much about them. Ouma did seem to acknowledge Amane Shinomiya due to his incredible Nameless Glory, as he described him as someone dangerous to Ikki and warned him of Amane's interest in him.
Bukyoku Academy[]
Yuudai Moroboshi[]
Yuudai and Ouma were rivals in their youth and competed in the Little Leagues. Despite seeing the kind of length Ouma had gone through, Yuudai still respected him and even didn't want to be called the Seven Stars Sword King since Ouma didn't participate in the Festival from the year before. Ouma though doesn't seem to care much about Yuudai, though still recognizing him as a somewhat powerful opponent.
Rokuzon Academy[]
Renji Kaga[]
Both Ouma and Renji were both rivals in their time as children in the elementary school with Renji still wanting to face Ouma again and spent the past five years training. He, however, didn't view Renji's efforts as such and even called all the time he spent training useless before mercilessly ripping out and crushing his heart. Though he still took him seriously in their fight in the Seven Stars Sword Art Festival as noted by Stella who noted that Ouma needed to go to such lengths to keep Renji down.
Rebellion[]
Adam Goetia[]
Ouma fought Adam Goetia, the Tyrant during his travels to test his true strength on the battlefield and despite fighting with all his might, he was unable to do anything against the one he viewed as a true demon. In the battle against the Tyrant, he felt fear for the first time in his life, and even to this day, Ouma is still terrified of him.
Union[]
Abraham Carter[]
During his initial encounter with Abraham, Ouma wasn't interested in facing him, but it changed after realizing that he was the person who attempted to kill him under the alias of the Tyrant. Instead of fearing him, he faced the desperado with confidence believing that he could defeat him. He soon lost interest in Abraham after witnessing what he had done to Rinna and Sara, and didn't relish in his victory against his previous foe.
Other[]
Edelweiss[]
It is unknown what he feels towards Edelweiss, but it is elaborated that he had some hint of respect and gratitude for her saving him when he was groveling at the feet of the Tyrant. He viewed her swordsmanship that Ikki stole from her as a "gift". It is even possible that Edelweiss teaches him something due to their similar speeches about fate.