Add npc Jimbei for the fish-man race to unlock the fighting style.
Improvements of Sanji's style, since it is impossible to complete without using the fruit, you can try adding a larger radius of his attacks as well as increasing damage when using haki (the appearance of fire).
Admirals as a boss

Addition of magma fruit

Addition of Garp's style using haki in close combat

Development of haki and not only from falling out of bags, i.e. each level add +10-50 haki
also races do not work
Addition of more accs for haki before killing the moon lord

Addition of Shanks npc for pumping royal haki
Addition of the giant race (increased damage, lower movement speed)
Addition of Teach as a boss in hard mode