I picture
Indigo-Paul as the prisoner-turned-medic of the Secret Society, or Injustice League, or Legion of Doom, etc.
To be fair, a lot of DC villains "
had one bad day" that started their slippery slope into villainy, so Lex Luthor or Gorilla Grodd might play on Indigo-Paul's bleeding heart sympathies to keep him captive and under control. Much like Panacea and Othalla in "Worm", a healer is priceless to people who get beat up fighting/committing crime and don't want to spend months recovering from injuries.
Question: What's the opposite of Florence Nightingale Syndrome
when you develop feelings for your doctor, nurse, or caretaker? Cheetah, Giganta, Killer Frost, etc.
Link:
Emergency Transformation - TV Tropes
Other possibilities: Indigo-Paul is injured when the Justice League attacks the Secret Society's HQ. Cheetah performs an emergency transformation* on him to save his life at the expense of turning him into a
cat-man.
*The JLU version of Cheetah was a scientist who tested her theories on herself,
putting her life on the line for the sake of developing new medicine.
Cheetah: "
Do you hate me for doing this to you?"
Catman!Indigo-Paul: (flexing in front of a mirror) "
Sorry, I can't hear you over how ripped I look. I could grate cheese on these abs."
Killer Frost:

Catwoman: "
Me-ow!"
Cheetah:

"
Back off, I have first dibs!"