I don't need a drama to have a happy ending, that's not at all why I dislike the ending of DAS so much (other than me having basically hate watched a drama for the first time overall) but the ending of Duty After School didn't feel earned. Had they all been massacred by the aliens I feel like much less people would have complained about the ending, even though it would have been just as sad. I think the issue comes up with this decision clearly having been made in the last two episodes. While yes Yeong Soo had been established from the get go as weird and a bit of an outcast at times, none of his behavior previously was showing signs of being prone to psychosis, sexual assault or violence. So to be faced with a character suddenly doing these things from a viewer's perspective is odd.

From a character perspective or even real life you definitely never know when someone will snap, you might even call the sudden change realistic in that case but again, we are watching a drama, we are a viewer from the outside who thrpughout the drama always had a 3rd perspective on everything happening with details unbeknownst to the characters. So based on that perspective it didn't feel conclusive. Instead it felt like they were suddenly looking for a reason to give the viewers a shocking ending. Especially the way it cut immediately to the end of the literal apocalypse with the solution to the very problem they spent 8 episodes fighting being mentioned on the side with a quick "Oop they developed a new weapon and now all is well." Those two aspects in combination were jarring when you just spent a whole drama watching characters being focused on survival just for it to all end abruptly by something they didn't spend time building up to.

There is of course so much more wrong with the drama than the ending but I don't wanna write more paragprahs about all the plot holes, strange characterizations or bad chemistry. In the end the acting is really great, the premise is fun but the drama succumbs to a lot of bad choices and for me personally, a lack of relatable or even just sympathetic characters.