Spencer Reid X Former Hitman/ assassin
Oc/Reader is a extremely talented killer, she was raised in a broken home and manipulated into becoming an Hitman/assassin. (Something like that)
She is a legend and the best in the business, with other hitmen/ assassins being terrified of her they call her the (codename)
She is muscular (has to be as she is a fighter) and is covered in scars and has multiple tattoos.
She Meets Spencer at a book store and they start talking after Spencer spots her book and he starts rambling facts about it and unlike others she asked him for more fact being genuinely interested.
They talk for weeks before she asks him out on a date.
They go on a fabulous date and become official after a couple more dates.
Spencer told her about the BAU but she tells him she used to be a personal guard and that she is now retired.
Spencer keeps her a secret from the team especially Garcia who is horrendous at keeping secrets.
After about a year of dating Oc/reader is truly in love with Spencer and wants to start a life with him so she retires from the business.
She never tells Spencer her secret.
Until a family member of someone she killed comes for revenge kidnapping Spencer.
And sending her videos of Spencer being hurt. She goes to her hideout bringing our her gear before going after the son of a bitch who took Spencer.
The team is worried as Spencer isn't responding so they go to his home, and that's when they find out he is in a relationship.