In Deadly Premonition 2 you get your standard incest plot with a side of transphobia since the brother in question here is actually a trans woman. The game came out in 2019 but feels like it was written in 2005 with how the character’s gender is handled
The game is just all over the place. Swery wrote an incestuous perverted trans murderer and constantly misgenders her but also has several scenes where Francis York Morgan chastises small town hicks for their transphobia 
Obviously Swery didn’t consult anyone while writing the game and it’s interesting no one in the localisation/translation team flagged these issues in the script either. Swery got predictably pilloried on Twitter when the game came out on Switch and they scrambled to patch the game to make the dialogue less offensive. Yes, the PC version you see here is the patched version of the game 
Aside from all the transphobia, there’s plenty of other iffy shit going on with the game’s writing. The main villain is building up to be a black guy and his monstrous, morbidly obese blonde wife which feels a bit weird with how many of the game’s black characters are written, like the black lady who starts every sentence with OH LAWD. There’s also a running theme of older male characters being in love with much younger female characters, the most extreme example being a 16-year-old girl dating an adult man that looks to be in his thirties which is NEVER REMARKED UPON and treated as completely normal. York also has a 10-year-old girl sidekick in this game and some of the shit he says to her just comes off as really fucking weird sometimes
Francis Discord Mod Morgan
I’m nearing the end of the game and it’s just shocking how bad Deadly Premonition 2 is compared to the original. The graphics and gameplay being absolute dogshit could be explained by the game having basically no budget but how the fuck is the writing so awful when that was the glue holding Swery’s previous games together
Ooo I actually know the answer to this one.
So, originally this wasn’t a thing. Back in the day almost every anime had a “childhood friend” of the family who was extremely close to the protagonist’s family. So much so that they would come and go at the house as they pleased, they behaved like siblings. This character was usually filled the “love interest that deserves to win but always loses” role, and the protagonist was oblivious to their love. A recent show called Blue Box actually brought back this archetype with a twist in that they actually physically live together.
Anyway as this childhood friend archetype phased out, writers still wanted a “love interest that perpetually loses” character in their stories. And since this character was pretty close to being a sibling in terms of writing to begin with, they just straight up made it into the sister, the character who harbours a secret love interest for her brother, but it’s taboo, and her brother will go and date [real love interest] anyway.
It was Oreimu that popularised this and spun off hundreds of imitators. Some others did it first but it was after Oreimu’s popularity that it became completely pervasive.
To explain why writers use this so much and put this another way - it’s a love triangle trope where the female love interest is on the inside and has more access to the protagonist than the other female love interest. The way this evolved into the sister of the male protag is actually pretty obvious when explained this way.
And the more it’s depicted, the less the topic becomes unusual to see in anime, so the more likely it is to just be acceptable and normalised in the medium, so you have other incest shit being depicted outside the love triangle / loser-love-interest trope now as well.