How would you go about subverting the player's expectations?

I didnt mean to strike a cord, just my perception, I personally watch alot of anime and based on your avatar I'm guessing you do as well and there were MANY times I watched an anime believing it was going to be lighthearted and fun and then it took a horrific turn for the worst and it both subverted my expectations as a viewer as well as shocked me but not in a bad way.

For an example theres a new and ongoing anime even right now called Goblin Slayer that'l started extremely positive and down right generic and within 15 minutes everything absolutely flipped

It doesnt have to be exclusively dark either, the series "vikings" does a great job incorporating all types of violence with great Detail but not overselling the subject.

We can agree to disagree but I believe gore/sexual assualts have their place and, to get back to the root of it all can be tastefully done, that was the point I was trying to make.

How about a character that had a stable childhood with fair and loving parents, grew up without major mental issues, is aware of his/her own virtues and defects, knows his/her limitations but is also confident enough in their strengths, is not afraid to ask for help when needed, and admits their mistakes before working to correct them or make amends?

Bet that would blow any player's mind.

Rofl what a twist

I think we're kind of in a weird time with how our audiences build their expectations. As people become more genre savvy they begin to understand and recognize tropes more easily, and because of that I find that things that would have seemed like huge twists a few years ago are slowly becoming commonplace, while things that would seem a bit too tropey are starting to become a bit more uncommon. As a bit of an example, I watched the first episode of My Hero Academia a while back, going in only knowing that it was a show that was trying to ape the feel of a western superhero comic book. As someone that reads a lot of superhero comics, the moment I saw the show's Superman stand-in I immediately said to myself "ah-hah! he's the main villain of the piece!". See the thing is, superhero comics have done the "superman is actually a villain" thing so frequently now that I was actually surprised when it turned out that the show's version was an actual hero who just wanted to help people.
Ok so rant over, now what does this say about subverting expectations? Well, I think that as people become more aware of the tropes of a genre, and begin to build expectations for possible twists and turns in the plot, we need to be able to be more creative and work around those newly created expectations. I think that one of the best ways to do this is to take a trope and inject another trope into it. For example you might have a standard RPG forest level that also happens to be the fire level. Or maybe your main character is just a standard npc in a town, and he starts his adventure to get away from all the chosen ones that keep trying to sell him crap weapons.
For example, the Bard's Tale game from the early/mid 2000s took the idea of a chosen one and turned it on its head for humorous effect. Throughout the game you come across tons of young farm boys that all claim to be the chosen one. At one point you even come across a cage full of them. Of course, your character's entire reason for being on his quest is to get laid and he has no interest in fulfilling prophecies or any of that nonsense.
Something else worth noting is that Brandon Sanderson has a lecture on youtube where he talks a lot about the subversion of the reader's expectations, specifically in relation to characters. Not sure if that really helps or anything but he definitely knows what he's talking about better than I do.

A lot of this really just revolves around understanding your audience and leading them in the direction you want them to go. You want to lead them along the story by the nose, believing one thing while hiding the clues to the truth in plain sight along the way. Subverting people's expectations isn't about big twists or surprise endings, it's about the mystery. We weren't surprised that Atlas was really Frank Fontaine because it was unexpected. We were surprised because it all started making sense. When you realized you were actually Revan, all the pieces clicked. Hell, even the tragedy behind the Ice King from Adventure Time had a greater impact because of the subtle way they did it. In a kid's cartoon no less!

another great example of this is a film called "book of Eli"

I found delving into old sci-fi/fantasy short stories from years ago a great way to find a lot of plot twists to a character and story line. I had built a basic story line for my game and after reading a few Isaac Asimov, Ray Bradbury, H.G. Wells and Terry Brook novels as well as some assorted short stories I was able to come up with some great side lines, and yes, plot twists that the player wouldn't expect

One of the best subversion ever done in a game was a game that carried some pretty heavy plot points, a story that was at least partially inspired by the atrocities of WWII. It covered racism, slavery, abuse, and all manner of things that are the stuff of nightmares. Real nightmares.

Now the reason this subverted player expectation, and even had a lower tier ESRB rating, was that the developer remembered something very important. A game is a visual medium, and the visuals simply did not match the horrors that the game covered. Not only did they not ever really show the horrors taking place to any level of "ick," they went so far as to use colors and styles that were very pleasant to any player. The other trick that was utilized is that the horrors, while described well, were offset by the current quest/mission/task.

I am talking, of course, about Tales of Symphonia. On the surface it looks like a very normal JRPG where the graphics are done in a very pleasant cel-shaded style. Everything is painted towards a light-hearted RPG, even late in the game. Yet, the topics covered are really dark. This title doesn't stand out just because it's a great AAA title, but because it is the "gold standard" of player subversion. My kid at the time loved the game, and I did too -- just for different reasons.

The game went so far as to cover slavery/concentration camps in the forms of "human ranches," but the storytelling was done in a way such that it was never presented in a way to gross out or shock the player. To this day, it still amazes me how they managed to cover such dark topics with a candy-coated shell.