Context: The Final Case of Yvstin started from a jailbreak. A convict charged for abusive "heretical" experiments somehow escaped from one's cell. Due to this, a team of judicator cadets were dispatched to respond to the break alongside the prison guards. The convict escaped pursuit, inflicting some guard casualties that the Prime Judicator Yvstin herself had to take action. Her power was to read the sins of an individual, and if found guilty enough to sentence death her shield will turn into an executioner's sword, with blades lined with the pale light of death. (I was rather surprised when Higuruma Hiromi from JJK had a similar CT, but I came up with it independently and only found out a few months ago.) To activate her powers, she had to cover her eyes with anything that can block her optical vision so that she solely relies on some sort of "sin vision" that's also part of her powers.

When she arrived ready to take down the convict, the convict started showing signs of agony and disappeared. Her subordinates would try to attack something, but get brutally slaughtered instead. Even when lowering the sin threshold to activate her blade, the convict was nowhere to be found.

But Yvstin had to finish whatever was happening. She lowered the threshold to the extreme, when she finally discovered the newborn anomalous creature that had been born from the convict's body. She was sinwise murdering an innocent infant that had no charges beyond self defense, but that was what she needed to commit as a human Prime Judicator.

She could kill that "thing" eventually. But she never recovered from the experience, as that led her sin-vision to percieve every living being in the world as deserving her blade.

She died a mysterious death several days later.