A slice of life show harem romance expect instead of focusing on the main character it focuses on the stereotypical "idiot best friend" character. The series would start off as your typical slice of life but slowly get darker as the self esteem of the idiot best friend is destroyed and the reality of his life starts to set in.

His only existence is to be a joke. His best friend has multiple attractive women chasing after him and he's left making stupid jokes while others laugh at his failures. He starts to feel as though nobody, including his best friend since childhood really "likes" him but instead merely tolerates his presence. And speaking of his best friend why is his life so much better? He's a bit of an idiot but things seem to always go his way, and his life is pretty decent overall. Not to mention the attractive women that chase after him for seemingly no reason. Idiot best friend instead has no future, romantic life or even a life at all outside of relationships with people that don't even seem to like him all that much.

I'd see the show as offering a darker look on a character that's 99% of the time just a comedic tool to be mistreated and just fail at everything he does while meanwhile spending all their freetime with someone whose life appears much, much better, who succeeds at basically everything he does eventually. An environment like that doesn't seem healthy in the slightest yet shows never really focus on problems that could arise from it. The character is just meant to be abused in an amusing manner and contrast the life of the main character with his own. I thin it'd be an interesting look at standard harem tropes from a different view point.