How are we interpreting 'Justice'? Are we going for the basic "What is fair?" definition?
Jyggalag? I know he represents order, but you can't have order without a good justice system.
Jyg represents perfect order, literally everything must be in perfect order and the only way for this to be achieved is to make everything into a single static whole. I'd say you can't have justice without some disorder, which Jyg prevents.
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Honestly, I'd go for Peryite; he represents a softer order than Jyg.