- “She's like the little sister I never wanted.”
- —Dean about Charlie.
Dean and Charlie had a close friendship, which developed into an 'older brother-little sister' relationship, with both commenting that they see each other as siblings.
The pair have multiple similarities, such as a love of pop culture, a habit of making references to said pop culture to reflect situations they find themselves in, and a very similar taste in women.
The Girl With The Dungeons and Dragons Tattoo
Dean and Charlie first met when they confronted her in her apartment. Charlie was initially terrified, having read Frank's encrypted hard drive, revealing what was going. After talking it over, Charlie agreed to sneak back in to delete the files, with Dean (and Sam) guiding her. He also tutored her on flirting when she had to convince a guard to let her past. Following Charlie being confronted by Dick and another Leviathan, Dean along with Sam broke in to save her, while the ghost of Bobby took on Dick. Sam carried Charlie to safety (as Bobby had inadvertently broken her arm). She later said good bye to the two, and although wishing never to see them again, they parted on friendly terms.
LARP and the Real Girl
Mysterious murders by an invisible creature brought the brothers face to face with Charlie again. After their previous encounter, Charlie got into LARPing and was the "queen" of an army. Along with Gerry, Charlie and the brothers hunt the woods for the creature. Charlie was kidnapped by the creature who was revealed to be a fairy. They take down Gerry who was controlling the fairy and save the day. Even though Dean hates all things geeky, he dons the LARP costumes and "fights" side by side with Charlie, rallying her "troops" to victory with the speech from Braveheart.
Charlie e-mails the boys claiming to be in the area, with a case for them to work on. Directing her to the base, Sam and Dean learn from Charlie that she’d taken an interest in hunting, and followed all their exploits in the Carver Edlund books, before stumbling on a case of a man with liquefied internal organs. With Sam in no condition to hunt, Charlie volunteers to accompany Dean on the case, proving her competence on the firing range and dragging Dean through an honest-to-Chuck montage of outfit-shopping for her new FBI role. The two also talk about the problems that Sam's having with the trials of hell, Charlie trying to make Dean feel better. On the case, Charlie has trouble playing along, but manages to slowly find herself, however is kidnapped by a Djinn and is infected with Djinn poison. As a testament to their friendship, Dean takes African Dreamroot and joins her in the dream to save her. Discovering the dream is a version of a video game Charlie hacked many years earlier, causing her to have to go on the run, where she has to protect the ill. Dean urges her to let go of her fears and accept the reality of her mother's condition. Although difficult, Charlie agrees and is brought to tears, Dean comforts her. This does the trick and they both wake up. Once again they bid good byes but not before Charlie tells him from all she has read, she knows they will pull through, encouraging Dean to carry on, they then share a Star Wars-esque moment before she departs.
Following Sam's plan of using the Men of Letters computer to track the Angels, Dean sent Sam to get Charlie. The two were clearly happy to see each other, Dean was however slightly worried when he found out Charlie had taken up hunting on her own, following Charlie managing to set her computer up to the Men of Letters database, the two faced problems with the Wicked Witch who had got free. During the confrontation, Dean tried to convince Charlie to go wait in the Men of Letters dungeon which was the safest place, but Charlie refused. As such Dean took Charlie with him, to his room to look for the key to Oz. The witch however attacked and threw Dean, she tried to kill him, but Charlie dived forward taking the blast, killing her. Dean shot the Witch and drove her off. Over come with shock and sorrow at Charlie's death, Dean was initially unable to accept it, then he called Ezekiel and told him to fix her. Ezekiel warned it would mean he would have to spend even more time in Sam, more than either of them wanted and would render him unable to help them with the witch. But Dean still forced him to resurrect Charlie. Later while possessed by the witch's magic, Charlie was forced to kick Dean in the groin to escape. However, when she stabbed the witch with the red slippers it freed Dean (and Sam). Dean was noticeably proud of Charlie for killing the witch, however, when Charlie confronted him on bringing her back from the dead, Dean assured her that she would be fine and was still her, but she couldn't tell Sam. Charlie agreed to keep the secret as he did raise her from the dead. Dean was also slightly worried when Charlie left with Dorothy for Oz, but nevertheless let her go, knowing she wanted to go her own adventure.
There's No Place Like Home
Dean investigates a series of attacks by what turns out to be Charlie's dark side. Dark Charlie tries to attract him to the darker side of things, tricking him into letting her kill Russell Wellington, the man who killed her parents and suggesting that Dean let her do it on purpose. While Sam and Charlie try to find a way to reverse the process, Dean fights Dark Charlie who tells him she learned all of her fighting skills from watching him. Dean wins the fight, breaks Dark Charlie's arm and beats her badly, despite knowing it will affect Good Charlie. Sam stops him from beating Dark Charlie to death and Dean is left horrified by his own actions. In the Bunker later, Dean avoids Charlie at first, but she hugs him and forgives him though he refuses to forgive himself. Charlie insists on helping Dean solve the Mark of Cain problem and promises that they will find a way and he will succeed as he's a Winchester.
Sam recruits Charlie to help him decode Nadia's Codex and the Book of the Damned behind Dean's back. Charlie is clearly uncomfortable with the idea, but reluctantly agrees for Dean's sake. She later tells Rowena that she sees Sam and Dean as her brothers. After figuring out how to translate the Book of the Damned, Eldon Stynearrives, demanding the Book though she only has her notes on it. Though Sam and Dean both tell her to give him what he wants, Charlie decides she can't do that, even at the cost of her own life as it means betraying Sam and Dean and giving the Stynes a source of unspeakable evil. Her loyalty leads to her being killed by Eldon, but her last act is to email Sam her notes on translating the Book so that he could finish her work to save Dean.
Dean cremates Charlie's body while reflecting on their times together. He then demands that Sam stop the translation of the Book of the Damned which he does until he gets Charlie's email and sees it as his chance to cure Dean. Dean's anger over Charlie's murder causes him to decide to slaughter the Styne Family. In his anger, Dean kills at least twenty people including Eldon (avenging Charlie's death) and his little brother Cyrus, who was not evil.