Let's talk about Erica Sinclair's character arc and development and how she embodies the whole theme of the show.
This is a (long) analysis into Erica Sinclair's character arc and how that ties into the main theme of Stranger Things.
So, we're introduced to Erica in season 2. We see her standing next to her mom as she takes pictures of Lucas in his ghostbusters costume. Right off the bat, she calls Lucas a nerd and establishes herself as someone who thinks she's above all that.
Throughout the season, we continuously see her call Lucas and his friends nerds, and she continuously makes fun of Lucas. This seems like normal sibling behavior, so we don't think much of it, but it shows us that Erica is not like Lucas. She doesn't like comics and fantasy games and video games. She's not a nerd... right?
In season 3, we see more of Erica. We are reintroduced to her at the mall. She's hanging out with friends and we see she's got a to-cool-for-you type of attitude. She takes advantage of the free samples at Scoops Ahoy and generally acts like a cool girl.
She continues to call Dustin and the others nerds as the season goes on and she's pulled into the Russian scheme, but we start to see a different side of her. She's only 10 right now, but she's going on and making smart negotiations, talking about child endangerment, and going on about capitalism, showing that clearly Erica is very smart.
She continues to make comments about them being nerds, at one point saying, "You're all so nerdy it makes me physically ill." To the audience, it seems like she's apart of the majority of society that looks down on nerds and other people who are different.
Then comes the turning point of her character arc.
When Dustin and Erica are in the vents, Erica calculates the distance and time it will take them to reach the elevator again at the pace that they're going. When Dustin realizes that she did all of the calculations in her head, he realizes that, despite her brazen attitude, Erica herself is a nerd, and he calls her out on it.
Later on, at the end of season 3, Dustin and Lucas help Erica embrace her true nerdy self by giving her Will's DnD stuff.
We see that Erica appreciates this, showing us that she seems to have accepted the fact that she is a nerd. She accepts that she does like things that might be considered weird or strange, and that's okay.
And we see that in season 4, almost 6 months after she received the DnD stuff and 9 months after she was forced to recognize that she is also a nerd, we see that she is happier than ever.
She's been living her truth for almost a year now. She's no longer hiding her true self, conforming to society's expectations, or pretending to be something she's not. She's still the Erica we know and love. She still has her spunky attitude and she's not afraid to speak her mind, but now she leans into that nerdy side of her. When we see her fill in for Lucas in the DnD campaign, that's the happiest we've ever seen her, and that's on purpose.
Now, we know Erica's character arc has been her evolution from looking down on nerds like the rest of society to embracing her true nature as a nerd herself, so let's talk about how she is the embodiment of the theme of Stranger Things as a whole.
Stranger Things as a show rejects the idea of forced conformity (which is explicitly stated in season 4) and it's a show for the nerds and the outcasts. It shows this group of nerdy, bullied kids and it makes them the heroes.
Not only that, but the show actively punishes people who look down on others for daring to be any different than how society says they should be.
So, overall, Stranger Things as a show is telling the world that it's okay to be different. In fact, being different has saved the world multiple times in this show. It's saying that embracing your true self, no matter how weird or strange, is better than conforming to society's standards.
And that's what we see with Erica. We see that she started out looking down on nerds, just like the rest of society, but once she accepted and embraced her true self as a nerd, she was so much happier for it.
Tl;dr: Erica's character development of going from a nerd hater to embracing being a nerd herself perfectly shows the message that Stranger Things is trying to send by showing the audience that when Erica stops acting the way she thinks she needs to act (looking down on those who are different/weird/nerdy), she's much happier.
