"Crimson Rose" is a gun-for-hire, one of the only two female gun-for-hires (five gun-for-hires in total) in Glitch City. She is one half of the so-called "Reapers", the other half called "Cobalt Lily". Both of them only take clients who are "resourceful enough" to find them and pay them a wealthy sum of money. Private detective Art is tasked with tracking her down.
Not much is known about Crimson Rose from what is given to us through the events of the game without triggering certain dialogue on certain days.
Art receives an envelope of money with the task of finding Crimson Rose. Please keep in mind that this is just Art's findings and may not be the complete truth. On Day 7, if Art doesn't run into Stella, he mentions that Crimson Rose is unstable. She was last seen at Apollo Bank; her cover blown (something that doesn't happen with her). It seems that she "got crazy with bloodlust" and killed a guy and left him disfigured. She's now hurt and on the run. Art says he doesn't want to get involved with this case anymore, no matter "how much they offer me".
However on Day 12, the client offered a huge amount of money, so Art couldn't refuse it and is back on the case. It's revealed that Crimson Rose's father and Art's client (most likely using a middleman) is Lord Lance Lavender, a big name from Kanyevania. Like his daughter, his blood apparently has some weird reaction to Glitch City's nanomachines. Once in contact with the air, it does nothing. But if still fresh and touching someone's blood, the nanomachines will initiate a reaction. Essentially, they'll just eat through the other person's body until there's nothing left. This is almost the exact same thing that Crimson Rose has.
Crimson Rose left years ago to earn her living here and he hasn't seen her ever since. Art couldn't figure out who the client was on Day 7 becase he had no clue who was making the contract, and tracking all the messages to the source would've been too costly. He found out the client was by knowing who the sender was.
Crimson Rose's blood has an abnormal batch of nanomachines. They react to the "normal" kind floating inside people (definitely humans, not sure about any other being). She kills people by letting her blood touch the blood of her victims, and it causes nanomachine rejection almost immediately. It rapidly spreads, "spreading as fast as your blood pumps." Tissues get ripped off by themselves., then brain damage. She never executes her targets (which means she probably wasn't hired by Ingram to kill the White Knight responsible for Ingram's daughter's death as he asked to bring the White Knight's head to him). She just cuts them, cuts her palm and holds the target's injury tightly. "Some say" the target looks like it's getting drained, getting thinner by the minute.
On Day 14 if you give Art the wrong drink twice he will reveal that he managed to track down Crimson Rose in her last moments. Unlike what she normally does, she stopped covering her tracks and Art found her sitting in a room of (likely) a drug lab near some corpses. She passed herself off as a prostitute and then proceeded to kill everyone inside the drug lab. When Art found her, she was "drugged to hell and back" and from what he could get out of her she was dying. The cause of it seems to be the same rejection she used to kill her targets was also killing her too. Art delivered her the letter only for her to tear it apart without reading it.
The reason why she did it, according to Art was probably because of her hatred for her father. She was born for experimental purposes; a living guinea pig for her father's condition. He was going to use her to test any treatment, no matter how unorthodox. She was experimented upon from an early age. And when she found out what her blood was capable of, she just snapped. In her own words, she realised that "I didn't have to take shit from anyone anymore, not even my father". She ran away from Kanyevania and came to Glitch City. That's when she started as a gun for hire. She got trapped in that bank and then, the rejection started to kick in...