Every character in The O.C. went through drastic changes by the time the show culminated. But no character experienced quite as tumultuous an evolution on The O.C. as Marissa. After all, she started out as a sweet, slightly rebellious girl-next-door with an optimistic outlook and a desire to see the best in everyone. It wasn’t until the trip to Tijuana, where she overdosed on painkillers while drunk in attempt to cope with Luke cheating and her parents’ impending divorce, that we truly got to see the dark side of her.
One of the main catalysts for Marissa’s swift personality change was, as said, her parents’ split. After Tijuana, she tried to pretend everything’s fine; she even took Ryan out window shopping. She lamented that with her parents' divorce, she wouldn't be able to afford the lavish lifestyle she’d grown up with, but was happy to spend the day with Ryan. But when she was about to go home, she was stopped by a security guy who asked to see her purse. Once he opened it and poured out everything, Ryan noticed that Marissa went as far as stealing an expensive watch that he had tried on.
It became clear at this point that their roles had become reversed — Ryan, who had initially been seen as a “bad boy” for his criminal past, was now the responsible, well-meaning one, while this marked the beginning of a series of missteps Marissa made throughout the show.
After that incident, Marissa attempted to get help by seeing a therapist. But all efforts of betterment were halted when she met Oliver while waiting for her session. Oliver is one of the most deeply hated characters from The O.C., and he wreaked havoc in the core group’s life. He preyed on Marissa’s vulnerability and tried to do everything possible to win her over — despite knowing that she was dating Ryan. Ryan eventually left Marissa out of frustration with Oliver’s meddling, and it wasn't till Oliver went as far as threatening to kill himself if Marissa didn’t leave Ryan that Marissa noticed how bad their dynamic was.
But even though Oliver was extremely toxic and emotionally abusive, losing a close friend left Marissa desperately needing support. It didn't help that Ryan also had a brief fling with ex Theresa and might've been the father of her child, causing him to move back to Chino. Not to mention that Marissa's mom Julie was also having an affair with the teen's ex Luke. This made Marissa turn to alcohol as she attempted to cope with everything.
And even though Ryan eventually returned by the second season, Marissa’s mental health spiraled as her relationship with her mom grew worse. Out of rebellion, she started hooking up with “ yard guy” D.J., knowing Julie would never approve of their relationship. She also began to date Alex, Seth’s ex-girlfriend. The way the show handled Marissa's relationship with Alex and her bisexuality has been deemed controversial by some viewers over the years, but the romance did help Marissa briefly change back into the girl we were introduced to in the first season.
Even though being with Alex didn't truly solve Marissa’s issues, Alex became a confidant and the support system she desperately needed. But the relationship ultimately ended when Alex realized that Marissa was still in love with Ryan. Sadly, after returning to Ryan, Marissa met his estranged brother Trey, who attempted to sexually assault her. Once Ryan found out, he ended up fighting with his brother, escalating to the point where Marissa had to intervene by shooting Trey.
This now very famous action caused the biggest change in Marissa’s life and behavior. Even though she was found to not be guilty because she shot Trey to save someone’s life, Marissa was expelled from Harbor, her prestigious high school, and had to face a new challenge: public school. She struggled with fitting in and befriended Johnny and his friends, introducing her to a brand new world outside her Harbor friend group. And even though she was eventually re-admitted to Harbor, she remained in touch with her public school friends.
But by befriending them, she inadvertently caused Johnny’s death when she wrote him a letter expressing how she wanted to remain friends with him instead of being in a relationship. After reading it, he drank to cope and climbed a cliff, falling to his death. Knowing she was part of the reason why Johnny died severely affected Marissa, causing her to engage in more harmful behavior than ever before.
She began to date Volchok, a character as intensely hated to this day by fans as Oliver. Her alcoholism reached a low point, and she began to experiment with drugs, too. After Volchok mistreated her numerous times throughout their relationship — including cheating on her at prom — Marissa decided to break things off. But he eventually drunkenly killed her when he found out that Ryan was driving her to the airport so she could go live on her dad’s boat.
While the other characters fromThe O.C. experienced positive changes throughout the show, Marissa unfortunately changed for the worst and had the most harrowing journey of all.