While specific to mature fan works, these platforms often host original action series or doujinshi that fit the "fight in this life" theme.
The idea of fighting in "this life" often implies a previous life or a transported soul fighting for survival in a new world. doujindesutvdoyouwannafightinthislife new
To help you find exactly what you're looking for, could you let me know: Is this a story (Isekai)? Are you trying to find a specific website to read it on? While specific to mature fan works, these platforms