A person is born with a certain amount of mana, or life-force, which steadily increases as they age. This mana allows our biological forms to function and is used to power spells in magic rituals. When a person dies, their soul is transported to the afterlife, where it is abosrbed by God and used as a living battery. Therefore, The purpose of a human soul is to gather mana during its life cycle in order to make God stronger. The physical form is used as a receptacle for the soul, which houses it and allows it to exist in the mortal world.
Even though a person gains mana throughout their life, their aging bodies prevent them from taking full advantage of it. There is a spell which allows an individual to steal the mana from other living beings in order to power themselves. When a person is murdered, their mana can be absorbed by their killer using this ritual. Unfortunately, while the soul is unlimited in storage capacity of mana, The physical form is not. Everyone has different limitations as to how much their form can maintain. A person that is born with a mana level of 50 will have a body with less capacity than someone born with a level of 300. If the former steals the mana of the latter using this ritual and adds it to their own soul, along with the mana that he will gain during his lifetime, the soul will absorb more power than the body can store, causing it to break apart.
The solution around this is to contain stolen mana inside a homunculus, an artificial human which lacks a soul. These beings are specially built servants that are built for variety of purposes and tasks, such as defending their master. Its main purpose is to house excess mana, allowing the mage to use it only when needed and eliminating the danger of absorbing it themselves. The problem is that a homunculus needs life force in order to function. Since it doesn't contain its own life force due to the fact that it is artificial, it must use the mana that it stores to power itself. This is a hilarious conundrum, for it must use the same excess mana that it was meant to contain as a means to make itself function, thereby making its creation pointless.
How can I build an homunculus to make it more efficient at holding energy?