This is a very interesting prompt. I don't know any show like that though. I'll look forward to reading everyone's answer.
If the question was "where the protagonist loses everything in the end", I may be able to name a show or two.

Do anti-heroes like Vincenzo count?

I know Stranger 1&2, Life, Blood Free, Grid had the antagonists winning substantially. But I equally appreciated that it wasn't only the people, sometimes the antagonists was the system and the people who utilize its flaws for their benefits.

Another antagonist winning I recall is Fly Dragon. This one had me quite emotional cause sometimes, I didn't even know what to feel about the episodal antagonists. Those people were unapologetic about their actions and they stuck to their guns, and won.

Another antagonist winning... I'll give it to the underdog On The Verge of Insanity. Very realistic take on the cutthroat corporate world. Yes, they got out of it. But, they essentially lost the fight with the company board. To our joy, they came together to found a saner work environment and it became successful.

The latest one is Uncle Samsik. I'm so sad he died without tasting pizza. I don't know which part of the victory the antagonists had hurt: that Samsik died, or that he died before tasting pizza. I don't know if the An Ki-chul counts as an antagonist but I was so angry when his doings were revealed.

Memories of Alhambra: The killing game won 😏 cc:@sicarius

This is a tough one. After all, these are K-dramas and, when they end poorly, it's usually because of poor writing rather than "surprise topsy-turvy endings" in which the antagonist wins. So, most of these are going to be judgment calls, I bet, rather than clear-cut cases.

That said, the prompt is careful--we are talking about antagonists not "villains."

I think there's a case to be made that every time a tsundere male lead doesn't quiiite make it into the audience's good graces, it could be considered a time when the antagonist wins. For me, this was true for SURE with Miss Night and Day. Gye Ji-un never came close to redeeming himself for me after his horrible workplace behavior towards Miss Day (Im Sun), and he also never really convinced me of any authentic affection for Miss Night (Lee Mi-jin) either. And yet, there he was, talking about how he deserved love, walking off into the sunset right there at the end.

A second way to construe the prompt is to focus on the times when the "antagonist" isn't necessarily a human but instead a supernatural force. In this case the most obvious example of when the antagonist "wins" is directed at Kim Shin in Goblin.

And, finally, if hated tropes/plot devices also count as "supernatural forces" who can serve as antagonists, then the prime example would of course be when noble idiocy killed Seon Woo-hyeol in HeartBeat.

I realized thinking about this that despite my love for more serious shows which often have sad endings, I can't think of many where the antagonists unquestionably "won". There are shows like Nokdu Flower, where the Japanese clearly win in the short term, but the show's ending points towards a future where that will no longer be the case. The only show I can think of where the antagonists' triumphs made me want to flip a table was Conspiracy in the Court, and that wasn't because they succeeded - it was because they succeeded not due to their superior planning or intellect but because their folks could run faster than the protagonists.

If the antagonist is the writer, there will be some that comes to mind and I do want to flip tables.

But in the story itself, none comes to mind right now.

My Country : Even if we knew about History, it hit hard.

Every drama about Japanese occupation? In Mr Sunshine, for example, the end was very bitter.

In Moving, I didn't really feel like the protagonists won... They were manipulated during their whole life.

My Country? The antagonist did win, but at what price?

No Gain No Love: The antagonist wins

The company: number one spot in the industry with one trillion in revenue
The FL: profits from her ideas in his company and invests in her startup
The ML: kicks him out of his company and sends him abroad
The secretary: never transfers him despite his promise and calls him a traitor for quitting to pursue his career
The girl: never breaks up with her or forced to be separated
The screen time
The spin-off

Hong Gil Dong's ending still haunts me. It was one of the first dramas I saw, and the found family there was lovely.

What inspired this prompt: I watched the japanese drama House of Ninja and was left😐 afterwards.

First, I thought the show was gonna be a family comedy about a family of ninjas who just use their skills in every day life. So as things played out, I started feeling a bit like "this isn't exactly what I signed up for".

Then the "twist" happens with the reveal of a certain character and I thought "hmm, okay". Maybe I'm just used to the return of characters so it wasn't *that* jarring for me.

HOWEVER by the end of the drama, the family who I thought were the protagonists ends up being played, ends up losing a loved one, lose their individuality, and are "doomed" to continuing following the rules of the organization for the rest of their lives.

Meanwhile, the antagonists played the long game apparently and eventually had things play out how they wanted and ended up in an even more powerful position, setting the stage for their further plans.

After I watched this, I was like what did I just watch? How am I supposed to feel?

The lead actor was also the writer or director (I don't remember which but this was *his* baby) and I think he said it was a story about family. That wasn't my takeaway. My takeaway was just feeling like... adrift? Like it didn't fit into a distinct box so I didn't know how to feel about it. I don't even know if I consider it a good show or not.

KBS’s HEARTBEAT (2023) (Amazon Prime). Imo the antagonists who won were the drama’s scriptwriters. They did Taec wrong.

EXTRAORDINARY YOU - the ultimate example of "rage against creator" trope. Yes, it's sorta happy for OTP in the end, but to call THAT a win?! Someone pls make a fanfic where The Writer of it dies from aneurysm mid-story, leaving plot forever unfinished and poor characters finally free from that psycho sadist's grasp...

The show hasn't finished, but I can't stop thinking that the Justitia/Bit Na in The Judge From Hell feels like the antagonist who wins every single time.

The ML "is the good cop" and she's "the serial killer demon". But he can't catch her. No matter how hard he tries.

I know we have the real "bad guys" hidden somewhere, but, right now, she's the one who needs to be stopped.

Since people find it hard to think of shows where antagonists win, I guess that's not much of a thing in kdramas?
Maybe it happens more in movies?

I haven't since Old Boy but I think what happens in it probably counts. Maybe Parasite also counts? Though I guess Parasite is more of an example where perspective matters.

Just like Kat, I’m thinking more along the lines of “what if the villain is the happenings and the physical demise (i.e. death) of a character instead of an actual character? Because this has definitely been the case for me in recent years of drama-watching more than anything (or anyone), especially for dramas wherein it’s in media res for the opening scene and we as viewers are already being given the ending to a certain plot point/scene/demise of a character, and the rest of the drama is just a giant flashback telling of everything happening before the drama’s opening scene in media res

Having just watched it, Gyeongseong Creature (Parts 1 and 2) are putting in a bid. In each case, the "human experimentalists" are not destroyed but live to continue their experiments; our ML and FL end up not remembering the other as a result of the experiments. Lady Maeda might be dead; her vision and work is not.

I once saw a European movie. I don't remember what country, but it was about three robbers who invade a house of a couple with a teen daughter. The robbers do every bad thing you can think of, and in the end walk off with the money, with all three protagonists dead.

I HATED the movie so much. I could not believe what I saw. I was like why...

I can't imagine having to watch 16 hours of such torture.

Mr Sunshine comes close. The Japanese won. I have often wondered if she would have even lived long enough to see her country get independence, and what she would think of the division.

seeing Seo In Guk here I could say 38 squad is where law wonbut that was ultimately our fraudsters goal. Like I understand he had to go to jail but... the bromance tho. and they stayed bros anyway, so... it is a little vague. but I like that it wasnt a villain against good guy but a system vs people who try to crumble it.

Joo Won first drama role, the 2ML in KING OF BAKING or Bread, Love, and Dreams. The character was not a nice person. And while he doesn't completely thwart the ambitions of the hero, he doesn't completely lose either and he gets The Girl.

You might say the antagonist won in Lucifer. Or no one won.