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.
Role in Super Smash Sisters
Souji is a non-playable helper in Smash Sisters. He can use fire and martial arts like Kyo. When a situation goes bad, Souji can set himself on fire to take his enemies out.