The concept of "Sword Art Online" wherein players are trapped in a virtual reality game and facing real death if they die in the game was initially rejected by publishers because it was considered too dark. However, when it was finally published, it became one of the most successful light novel series.
Wow, it's wild how a concept initially deemed too dark ended up becoming a hit like "Sword Art Online"—shows you never know what'll resonate until it’s out there!