When Thor looks at him, he sees a man who is and is not his brother. Cruel as Loki is cruel, tall and thin enough to snap with a smile to remind you he already has. Loki would not dress as a jester, Thor tells himself over and over. A mantra, a prayer to no particular god. Loki would not throw his head back to loose a laugh that has more in common with screaming.
When Thor first sees Joker's scars, the breath leaves him. He remembers Loki curling inward, choking on his own blood, unable to open his mouth even to vomit. He sees his eyes too wide, too wet, words poured out in an expression that can never encompass them. He watches Loki's body jerk where he kneels, nostrils flared, sobs strangled low in his throat to tighten there. Thor watches the threads threatening to pull his lips apart, and he watches Odin with his unspoken command to do nothing.
Thor remembers. Thor obeys.
When Joker moves closer, his mouth red with something like blood, his gaze black and unreadable, a knife gliding in again, again…Thor does not resist.
Maybe it's something like justice.