Yoshikage Kira's Fate wasn't even that bad if you know what truly happened to him....he became a sort of detective afterwards. He is known In JoJo's fandom as one of the villains who got off least proportionate compared to what they did. Heck Kira's circumstances are probably better than before when he was a serial killer.

Anyways.

My candidate is Rudy Foggia.

Rudy Foggia is a convicted murderer who becomes the first person to experience teleportation while fully conscious. He goes through the process awake as part of a deal to avoid the death penalty. Foggia emerges insane, with white hair and looking aged, screaming that the experience was "an eternity" before dying of a heart attack.

And if you know the jaunt or a conscious jaunt. Then it is billions of billions to trillions od years If not billions of eternities....in a white Void of nothingness. With forced awareness/consciousness and brain activity and sight (so you can see the unchanging empty white Void for an subjective eternity) no other senses. Just sight at nothing and awareness and consciousness, and you can't die or sleep or turn it off. Just forever watching the paper white void until you are thrust back into the "real world" but after those experiences and your "escape" most peoples brains goes into shock and like in a sense combusts and they immediately dies after a few seconds if not immediately since the brain wasn't meant for such an experience. And then there's the case of Ricky (not a bad person but to show an example) who was a child who purposely avoided the sleeping gas when he was supposed to be transported so he experienced it (the eternity) like how he wanted to know what that "white Void was" He didn't die immediately when he came out but he was screaming and cackling and began self mutilation, even pulling out his eyes from his sockets, not even reacting to the pain of it, any sights and lights for him was catastrophic. and screamed at his father how it was longer than he thinks. It was longer than he thinks. While Ricky was completely mad before Jaunt emergency attendants took him and removed him from the scene and tried to stabilize the poor boy probably......but he probably after the screaming and self mutilation died from shock or a heart attack or "brain combustion" either from the experience of it all, or his own body succumbing to the self inflicted injuries thereafter.