Jason was very protective of Cheryl. When they were younger, Cheryl always insisted on having a separate birthday despite the fact that she and Jason were twins, until one year, he convinced her to combine their birthdays into one. It wasn't until years later that Cheryl discovered that the reason for this was because no one wanted to attend her birthday and he didn't want her to be hurt.
When Jason learned his girlfriend, Polly Cooper, was pregnant with his child, they made plans to run away together and Jason enlisted Cheryl's help to do so, however, he refused to tell Cheryl about Polly or even that she was going with him, only that he wanted to leave and that he didn't want their parents coming after him.
On the morning of July 4th, Jason and Cheryl staged a boating accident at Sweetwater River, making it seem as if Jason had tragically drowned. In reality, Cheryl left him safe and sound on the far side of the river, with the promise that he would call her, however, a call never came. That morning was the last time Cheryl saw her brother alive.
Jason and Cheryl drove out to Sweetwater River just after dawn on July 4th and held hands as they walked towards the river. Cheryl asked her brother if he was scared, to which he gave a slight smile and shook his head, before pair the took a row boat out onto the water. Cheryl was later found by Dilton Doiley and his scouts, huddled by the river's edge, soaked, freezing and alone. She claimed to have dropped her glove in the water and when Jason tried to retrieve it for her, he accidentally tipped the boat and in his panic, drowned. Jason's death was later ruled an accident.
During an assembly at Riverdale High School, Cheryl spoke to the student body, holding a moment of silence for her brother and expressing her love for him. He was and will always be her soulmate, she proclaimed. She then told her classmates that she had asked that the upcoming back-to-school Semi-formal not be canceled, but instead that they use the occasion as a way to heal and celebrate Jason's life.
After the semi-formal, Jason's body was found by Kevin Keller and Moose Mason washed up on the shores of Sweetwater River, gunshot wound to the forehead. Later, as the authorities retrieved her brother's corpse, Cheryl looked on, shocked and confused.
The following Monday, Cheryl and her parents viewed Jason's body in the morgue prior to his autopsy. Upon seeing him, Cheryl quickly turned away, horrified.
While Sheriff Keller visited the school to inform everyone over the intercom that Jason's death was now being treated as a homicide, Cheryl injected to state that she would not rest until Jason's death was avenged. She was later confronted in class by Tina Patel and Ginger Lopez over the details she gave of Jason's drowning. Angry and slightly frantic, she told them what she told the police; that they both fell into the water, she made it to the shore, he didn't, and that was all she knew. However, she admitted to Archie Andrews that she thought his killer was someone they all knew. Cheryl later visited the Cooper house under the guise of befriending Betty Cooper. In actuality, she used the opportunity to question Betty about her sister, Polly, who had been sent to live in a group home following her break up with Jason. Cheryl believed that Polly could be her brother's murderer, however, Betty caught on and forced her to leave.
The night of the Pep Rally, which Mayor Sierra McCoy dedicated to Jason's memory, Cheryl raced off the stage in tears after performing with the River Vixens. She had seen Archie Andrews enter the field, red-haired and wearing Jason's former football jersey, which triggered memories of her brother. Distraught, she ran to the locker room where she was found crying by Veronica Lodge. As Veronica attempted to comfort her, Cheryl said Jason was supposed to come back, that she was alone now.
The next day at school, the results of Jason's autopsy came back and revealed that he had, in fact, not died on July 4th, but instead a week later on July 11th. As well, he had ligature marks on both wrists and his body showed signs of having been frozen for a time after death. The results directed the police to Cheryl who admitted she was guilty and was then escorted from class by Sheriff Keller.
Taken to Principal Weatherbee's office, Cheryl clarified that she was not guilty of Jason's murder, she loved her brother more than she did herself. She did, however, lie about the events of July 4th. She revealed that Jason's drowning was staged as he wanted to leave town without their parents following him. She left Jason alive on the Greendale side of Sweetwater River and he promised to call within a month when he found someplace safe, but Cheryl heard nothing from him. She also had no idea why he wanted to leave, just that he did. Sheriff Keller found that cruel but Cheryl defended her brother and when the Sheriff began to suspect her of making up more lies to cover her own tracks, Cheryl became frantic, proclaiming that she did not kill Jason. She then admitted that they had heard a gun shot that morning and perhaps whomever killed Jason had tried that morning and missed. The Sheriff, however, did not believe her. The interrogation was then interrupted by Cheryl's parents who angrily whisked her away.
The next night, Cheryl joined Veronica, Betty, Kevin and Ethel Muggs in their search for a secret playbook used by members of the football team to record their 'conquests', in an effort to combat the player's slut-shaming. Cheryl, however, did not believe the playbook was real, as her brother was co-captain of the football team and never mentioned it to her. After breaking into the school after hours, she was shocked when they found it and saw Polly's name listed next to Jason's, initially unbelieving that Jason would participate in something like that. The next day, Cheryl joined Betty as she burned the playbook, apologizing for anything her brother may have done.
In the days leading up to Jason's memorial, Cheryl took it upon herself to write a eulogy for her brother and fell asleep on his bed while doing so. She dreamed of viewing her brother's coffin and upon opening it, finding it empty, with bloody scratches dug into the lid. She then turned away to see a dead ghostly version of Jason reaching out for her and awoke suddenly, horrified. Immediately after waking, her mother found her in the room and banned Cheryl from sleeping in Jason's room again. As well, she banned her from speaking at Jason's memorial, as Penelope surmised Cheryl would only embarrass the family.
In an effort to end their rivalry, Cheryl invited Veronica Lodge to her home for a sleepover the night before Jason's service. While there, the two girls looked through a photo album and Veronica remarked that Jason was "crazy handsome" to which Cheryl agreed, affirming him as the "handsomest". She then told Veronica of the reason she wanted to do the eulogy she had written. Everything about Jason's death had been extremely public, with so much gossip surrounding his death and some people going so far as to say he got what he deserved. Cheryl wanted to let everyone know that she was sorry and that Jason deserved a better family than the one he had gotten and Veronica encouraged Cheryl to do the eulogy against her parent's wishes.
The next morning, motivated by Veronica, Cheryl changed into the very same white outfit she had worn the day she and Jason went out to Sweetwater River and hijacked the service just as it was set to begin. At the podium, she began by explaining that when she put her white dress on, it made her feel connected to Jason as if he were there in the room with her. She then told the guests about her and Jason's life together, that Jason had always protected her and Cheryl wished that she had protected him that day at the river. In tears, she held onto Jason's coffin and apologized for failing to do so before being escorted to her seat by Veronica. She later watched from afar as Jason was laid to rest in the cemetery on Thornhill's grounds, and imagined Jason was there smiling at her.
The morning after Jason's getaway car was discovered and subsequently set ablaze by an unknown someone, Cheryl learned that Polly Cooper had escaped from the group home she had been held at the very same night and surmised that Polly had to be Jason's killer. She immediately went to her mother with the information and a search party was quickly organized to find Polly, however, it ended unsuccessfully. Afterwards, Cheryl was present at a press conference held by Alice Cooper who revealed that her daughter, Polly, was pregnant with Jason's child, much to Cheryl's absolute shock.
The next day, Cheryl went to Betty and convinced her to let her help with Polly, who had no money and nowhere to stay. Cheryl explained that Jason's child was a game changer and that she and her parents would be more than willing to help. The next night, Cheryl arranged for Polly to meet with her parents at Pop's Chock'lit Shoppe, however, after an unsettling conversation with her mother regarding Polly's suitability as a mother, Cheryl arrived early to see Polly and was momentarily stunned upon seeing her visibly pregnant. Polly expressed her condolences to Cheryl, and took her hand in comfort, remarking that Jason had always spoken of how much he loved his sister. Moved, Cheryl warned Polly and Betty off and told them to leave immediately. Polly and her baby, Jason's baby, wouldn't be safe with her parents.
At the start of the maple season, Cheryl asked Archie to escort her to her family's annual tree tapping ceremony. It was an event that was meant to honor the Blossom bloodline and was something special that Cheryl and Jason had done together ever since they could walk. That year, she was not sure she could face it alone, without Jason.
During Jughead's 16th birthday party, while playing a game Cheryl called 'Secrets & Sins', Veronica claimed that Cheryl had loved Jason in a way that a sister should not and as Jason got older, he saw it as weird. In the end, he chose Polly over her and in response, Cheryl shot him in the head with one of her father's hunting rifles. Staggered by the accusation, Cheryl began to cry.
In the days leading up to Riverdale High School's annual Homecoming dance, Cheryl announced to Betty and the rest of the group that she was bringing Polly to the dance as her date and the two of them would be campaigning as co-queens of Homecoming Court. She explained that if Jason were alive, he and Polly would have been the ones crowned and it was only fitting that she run in his place.
While picking out jewelry from her mother's closet to wear to the dance, Cheryl discovered the heirloom ring that Jason had proposed to Polly with, which had supposedly been lost when Jason's car went up in flames. Angry and confused, Polly attempted to take it but Cheryl refused to give it up, even threatening her, "You are carrying precious cargo, but if you think for one second that those babies guarantee your safety, you're in for a rude awakening". Later, she questioned her mother's explanation of how the ring came to be there. Penelope claimed Jason had returned home shortly before his death and, wanting nothing more to do with his family, threw the ring in his father's face. Cheryl then told her parents that she had flushed the ring down the toilet so that there would be no proof should anyone ask questions, but secretly she kept it.
In the midst of Betty's search for the Sugar Man, Cheryl is asked of the Sugar Man, off of a lead from the Black Hood, who said that Clifford Blossom received supplies from the Sugar Man. Cheryl says that she has heard of the Sugar Man, as it was a story concocted by her mother, Penelope, in order to make her and Jason behave.
Cheryl confronts her mother about the Sugar Man, and Penelope denies the actual existence of it the first time, however, the second time, Penelope breaks down. She says that she concocted the story to make an all-too-real monster into a mere child's tale. Cheryl's father, Clifford, wanted to groom Jason into his successor, which, said by Penelope, commenced the events that led up to Jason's death.
Every town has one. The spooky house that all the kids avoid. Ours was Thornhill, the Blossom family's mansion, with its very own graveyard. And, trapped within its walls like some gothic heroine, was Cheryl Blossom. Still grieving for her beloved brother, Jason. Linked in death even as they were in life.
They had a very close relationship, with Cheryl admitting she considered Jason to be her soulmate.
They both have red hair, a trait which seems to be common in the Blossom family.
Even though Cheryl believed to know everything about Jason, he kept at least a few secrets from her (the list of the girls of the football team and Polly being pregnant. The real reason why he was running away from home).