So let's talk about Mikuni as Lady Justice. Lady Justice is the personification of the concept of justice, who is usually a woman holding a balanced scale in one hand and a sword in the other. Mikuni is often depicted with scales and his tarot card is "Justice". The shape of his lead is a noose that acts as a scale to weigh the sins of his prey. The woman in the center of his lead in its activated form is Kiriko, his mother. But his lead can also become a sword. When he goes for the attack in Chapter 144 "Judgment", Mikuni attacks his enemies with swords.
(See above, Mikuni with his scales (noose) and sword, with the number for the tarot card for judgment above his head)
In Greek mythology, there were two deities that represented justice: Themis and her daughter Dike. Themis was more about divine law and custom, while Dike was more of a personification of human justice and the enforcement of social norms.
Given that context, Kiriko is Themis and Mikuni is Dike in this metaphor. Kiriko agreed to an arranged marriage to Mikado per mage custom. She was happy to play the traditional supporting role as the wife of Mikado, the head of the Aliceins. When she was crossed by Mikado, Kiriko responded with the type of wrath associated with betrayed Greek gods. Even after the betrayal, she continued to play the customary loving housewife until she couldn't handle it anymore.
Mikuni, on the other hand, seems preoccupied with whether those who commit evil acts receive punishment. His lead only allows him to strike those who carry the guilt of taking human lives. He is akin to worldly judgment in that sense, like a ruler or a judge rather than an unknowable force of nature.
(This is the cover of Chapter 130, depicting Mikuni as a worldly ruler, likely from Lily's pov)
Mikuni's mirror world attempts to bend the world in a way that would support standard social norms. Children are cared for by their parents (Sakuya), siblings stay together (Otogiri and Johannes), parents are married and raise their children together (Akira and Touma), and spouses are always faithful to each other (Mikado and Kiriko).
Another thing to note is that Lady Justice's scales are intended to be balanced to indicate fair, impartial judgment. The scales are balanced on the cover of chapter 130. But in Chapter 144, Mikuni's scales are no longer balanced.
The scales lose their balance as Mikuni reveals his grand plan and his own perceived guilt for the death of his mother. The scales lose all pretense of impartiality when Mikuni states that true justice does not exist. The world is not free from guilt, and Mikuni acknowledges that he himself is not free from guilt. So Mikuni will become the closest thing to god in universe and abandon worldly justice for the sake of his own ideal world.
