You are inhabited by a world eater. While you are inhabited by the World eater and it is friendly you have exponentially increased healing even able to regrow body parts and close grievous wounds.

While inhabited and the world eater remains at full biomass you have advanced recovery, healing 1d4 physical damage at the beginning of your turn.

If your world eater companion is friendly, they can even heal grievous wounds and lost limbs provided it retains enough body mass. While inhabited and otherwise healthy you regrow organs and limbs at a rate of 1kg of biomass per day, costing your world eater biomass at the same rate.

The World eater gains biomass at a rate of 0.5kg per day when not regrowing its hosts body mass. It is capable of storing a maximum of 30kg of biomass at a time.

As an action you can command the world eater to accelerate your healing past its normal limits, at the cost of 3x the biomass your world eater can regenerate deadly physical wounds in seconds (up to dm decision how many rounds of combat it takes to heal based on degree and nature of injury). This ability takes 1 week to recharge.

After using this action, your accelerated healing is halted for 3 days while the World Eater recovers biomass.

Moreover your character no longer uses hit dice to recover but instead heals 1d6 hitpoints every 10 minutes while resting.

Your advanced recovery does not heal you while unconscious, but will stabilize you preventing the need for death saving throws provided you do not continue to take damage.