Casper didn't sleep a wink that night. Or the night after. He spiraled, his brain being his worst own enemy as he drank shakes, paced his apartment, and drank more shakes.
He hadn't felt okay before this, but having that whole interaction with Gunther had only made things worse.
The longer he remained on his own, without anyone else around, the more he fell down the rabbit hole.
Maybe it was a good idea that he left the Guild? If this was the response he was going to get, if this was how he was going to react, he didn't want to do this anymore. He NEVER wanted to hurt others, and he couldn't believe himself that not only had he considered hurting Gunther, but that he'd gone through with it.
