I'd just put a 18+ warning at the top of the chapter, or in the previous chapter warning people. It is what I plan to do. My novel is pretty normal, but there are a few sex scenes. Not something I'd label 'smut', but definitely not something my general audience would expect to read from my book.
No hate. Just thought it funny. I understand why he couldn't win the few battles he fought in but it looks really bad when you only have loses under your belt.
Like the concept though. Wrote a similar story with a fire user that is super OP that singlehandedly destroys a country with his...
i don't want to come off as shameless, but I think my novel, The Silver Path, has exactly what you're looking for. Dead on actually, though MCs' knowledge comes from another world, not previous life. Check it out, its just over 200k at this point...