I know this might sound repetitive, but I never quite understood the logic behind these games.
In the first game, the MC gets NTR’d by his wife with Shimomiya while he’s in a coma. Then, I found out he was beaten up by Kaede, who had always loved Naoto. Afterward, Naoto divorces Aya and gets together with Kaede, which should have been a happy ending.
However, in the next two games, we discover that Naoto has developed a cuckold fetish and ends up losing Kaede, who falls for Shimomiya.
Even though it seems unlikely, she actually falls for the ugly fatty. The DLC was created to try and justify this development, showing her internal struggle.
I have to admit, Kaede Dangerous Change still lingers in my mind to this day, which proves it was effective... but at the same time, its conclusion disgusts me to no end.