Souji Kusanagi is a member of the Kusanagi clan. He was chosen to represent and lead the Kusanagi clan for his generation, but he was afflicted with a similar disease to Riot of the Blood for unknown reasons. With that, he chose to stop training and fighting, afraid to become something like Iori Yagami. Souji moved from Osaka to Tokyo and was studying there. When Kyo was having doubts about his fate of sealing Orochi, Saisyu showed him a picture of Souji during that wild state and told Kyo to go see him in Tokyo, so he can receive his answers.
When Kyo arrived there accompanied by Shingo Yabuki and Athena Asamiya, he asked Souji about that strange picture of him. Souji then told him his secret: he said that the Kusanagi power possesses a dark side and, when Souji pushed himself to his limits to become the best Kusanagi there was, he crossed the line to that dark side and lost control of himself. So, afraid of becoming a wild beast again, he retired himself from fighting.
Telling his story to Kyo, Souji asks him to find his sister Aoi, because they have argued and she ran away from home. Kyo agrees and finds her in Osaka. Souji goes to the Kusanagi dojo where Aoi was waiting for him. After a small discussion, they reconciled and went back to Tokyo.
In one of the credits pics of KOF '98, Souji is seen training with Kyo and Saisyu.
Highly respected by his cousin, Kyo calls him 'Souji-sama'. He is more thoughtful than Kyo and wants to protect the Kusanagi clan.
- Pyrokinesis - Due to his Kusanagi heritage, Souji can control fire. He can create fire from thin air, create fire balls, deliver punches of fire, create pillars of fire and put his own body on fire. He is not immune to other types of fire. He cannot control other fires that he didn't create.
Souji fights with the Kusanagi style of ancient martial arts, a Japanese style of empty handed combat taught only to the Kusanagi. Akin to Kyo however, he too also knows the Aragami and Dokugami techniques.
- The King of Fighters '98 (in one of the ending pictures)