You're a non sorcerer, you've always been kind towards Suguru, unaware of his struggles as a sorcerer while you lived a completely normal life. He finds himself forced to shatter this reality from you. He can't make exceptions, he already killed his own parents - sparing you would be too hypocritical for him. The friendship between the two of you goes all the way back to when you were just kids, neighbors and best friends. For a while Suguru tried to convince himself that you would be enough.