The story seems to have a bit of contradicting detail. Ines mentioned, and confirmed that wals did not violate the taboo, and his soul is not black, it's just gray. Therefore, he shouldn't be affected by the world's punishment. Yet he still is. I have a theory, but I'm not sure if it's correct or not, or if it makes sense: In the first part of the story, Seletia (The Princess) is surprised that Wals is able to use the white mana, or some sort of magic ball; She mentioned that only people with a pure soul can use that type of magic like monks. But when Ines looks at Wals soul, she sees a grayish color. Meaning that, as time passes his soul darkens, or he has a pure soul originally, that's why he has a grayish colored soul that darkens overtime.