When are you going to throw in a time skip? He has been beaten down mentally and physically and it has only been a single day for the plot yet nearly 20 chapters have flown by.
Don't make sara good we want to see the mc taking the revenge and I have an idea the mc can take of the sea stone using the inventory and practice his devil fruit
Have him become the king of the slaves so his conqeuror haki becommes stronger. also you know heal the four girls and make them idolise him so when they escape he can go to Amazon lily and learn his haki