[... To grow the pocket world size, you have to use death energy related treasures, or wait for the world to absorb energy from the world around.
The rate of absorption depends on the overall size of the pocket world outer surface. For example, the one mile radius pocket world will absorb death energy from one hundred mile radius around it.
The wider the area the pocket world can absorb death energy from, the faster it will take for it to mature.
With a basic area of one mile radius, the pocket world will take from one up to three years to mature. Increasing its area will shorten this duration.
The seed can be transferred between owners, but if used it can't be moved again.
The owner determines who will enter and exit this world. No matter who, no one can enter the world without the owner's permission.