An athletic student who, along with Kureha, was transported to the dream continent, End Earth. Souma is in love with Kureha and is sometimes annoyed at Kiriya for not noticing her feelings for him. He then confessed his love for her, which apparently was not mutual, shortly before being transported to the other world. After seeing Kureha presumably die, he was able to pull out a legendary sword from Kureha's body. Souma turned out to be a 'Soul Blader', which is a person that can form a sword from the heart of a person he shares emotions with. Unlike Kureha, Souma would rather stay in End Earth, as he believes that it is the right place for him and since he thinks that he can be "together" with Kureha.
He later had Kiriya and Seena take care of Kureha while he wanted to take care of a few things on his own. Though he is a Soul Blader, he no longer wanted to use Touka's heart since he knew that her heart loved Kiriya. Instead, he started to use a katana.
When Souma and Kureha were between dimensions, they were greeted by Zero, who entrusted Souma in guarding the world from then on. Souma received one of the two twin dragon rings from Zero. (from Wikipedia)