- "I knew them back in the day. Canary, the Arrow, the whole crew. Honestly, I don't know where I'd be right now without them. They helped me out of a couple pretty tight spots. I owe them a lot. But I, uh, I saw the toll that it took on them. Like, people like to debate about the legalities, but for the people wearing the masks, it's--it's not philosophical, it's real. And it takes everything from them."
- —Cindy Simone[src]
On May 10, 2008, Cindy went to a sports game with her father, where he took a photo of her that he kept his wallet.
At some point, Cindy began using the nickname "Sin".
Working with the Canary
After the Undertaking, Sin was attacked by a group of men attempting to harass her, but was rescued by the Canary. Afterwards, Sin became the female vigilante's confidant, leading to Roy Harper being pointed in her direction when looking for the Canary. When asked about her, Sin led Roy to the Canary's hideout and knocked him out. When Roy woke up, Sin looked on as he was questioned by the Canary, but she let him go when The Canary assured her that Roy was harmless.
Sometime later, Sin ate breakfast together with Sara as they reflected on their families. She later encountered Roy again and met Thea Queen, and she mentioned to him how Thea didn't know about him being The Arrow's sidekick. When "the Mayor" attacked the event they were at, Sin was wounded and was saved by Roy and Thea. As she was recuperating at a hospital, she was looked over by Roy and Thea. She woke up later and told Roy that, because he saved her, she would keep his secret. She commented on how Roy was an idiot, and Thea wholeheartedly agreed, leading to Sin admitting she had begun to like Thea.
Not long after this, Sin told Roy and Thea of her friend, Max Stanton, who had gone missing for a week. She asked Roy if he knew someone that could help, but Thea commented that Roy could, and the three of them joined in on a search.
A Mirakuru-infected Roy approached Sin to show her the effects the Mirakuru. Upon hearing of a sleazy lawyer who murdered prostitutes being around the area, Sin posed as a hooker to entice him. When the lawyer approached her, Roy appeared and started to pummel him. Sin was able to calm Roy down and then called 911 to get the judge to a hospital.
After the Canary's identity was revealed to her friends and family, Sin attended a welcome home party for Sara Lance, and when she was introduced to her (the others not knowing of their friendship), Sin was quick to hug her, arousing suspicion among the others. Later when Sara had reconciled with her family, she reassured Sin that despite her having her big sister back, she would always consider Sin as a little sister.
Later on, Sin once again encountered Roy completely under the influence of the Mirakuru. Sin attempted to stop several people from attacking Roy, as they misinterpreted the situation. Roy then pushed Sin to the ground and she later told Sara about Roy, citing that he didn't seem like himself. Just as Sara was leaving Starling City, she and Sin shared a hug.
Saving the Glades
During the uprising of the people of the Glades against gang control, Sin witnessed Roy fight off Danny Brickwell's goons alongside a blonde vigilante who resembled the Canary, making her wonder if she was Sara. Later, Roy called upon Sin, along with the rest of the Glades' residents to stand up to Brick. During the fighting, Sin spotted the Canary and realized she wasn't Sara. Later, following Brick's defeat and the subsequent return of the Arrow, Sin informed Captain Quentin Lance that the woman taking on the guise of the Canary was not Sara.
It is unknown if Sin ever found out of Sara's death or resurrection.
Sin is a fiercely independent and confident young woman. Initially like Roy Harper, Sin resented the upper-class, believing all of them to be greedy, arrogant, and selfish. However, being saved by Thea Queen, Sin developed a newfound respect for the former. Sin initially disliked Roy for associating with Thea but eventually developed a friendship with him, playfully referring to him as "Abercrombie".
Sin deeply cared for Sara Lance, with the two developing a sibling-like relationship. Their bond was so strong that Sin was able to deduce that Laurel Lance, who had taken the identity of the Canary, was not Sara.
- Acrobatics/Free-running: Having grown up in The Glades, Sin has shown to be very agile and nimble, able to leap over a fence and scale a railing to quickly escape from Roy Harper.
- Skilled hand-to-hand combatant: While unknown to what degree, Sin has shown to have some rudimentary fighting skills due to living in a rough neighborhood; she was able to take down several of Danny Brickwell's men with little struggle.
Behind the scenes
- In the DC comics, Sin was an adopted daughter of Black Canary and was hunted by the White Canary. On Arrow, however, Sin is a friend of Sara Lance, who is both the Canary and White Canary later on.