During the course of the game Luffy will take a fair amount of damage making knowing how to heal in One Piece World Seeker vital for replenishing his health so you keep him alive. Knowing how to heal means learning how to use the game's regenerating health mechanic. Unlike other games where players are given healing items or restoratives for regular use in One Piece World Seeker health will regenerate at a fixed rate after successfully avoiding damage for a short period of time.
There will be occasions when Luffy is involved in battles that take place in confined spaces when this will be difficult to do. It is therefore recommended that in those situations when your health starts to run low you pull back and revert to Observation Haki mode so you can dodge incoming enemy attacks. You can also use this move to regenerate health while avoiding the enemy attacks. When you need to buy time to recover health take advantage of your environment by finding things to hide behind or circle around until you have enough health to get back into the game.
You can increase the rate of healing by as much as 100 percent by adding skills from the Parameter skill tree. You may want to consider grabbing these skills as soon as possible as doing so will considerably decrease the amount of time you will have to spend dodging and hiding while you wait for Luffy's health to recover.