Infinite Contract: Starting from the Mechanical Maid

Infinite plane search, fight and retreat? The entropy of this world is constantly being lost, adding firewood to the world to continue its life: crossing the gap and bringing back anything from another world, even a handful of soil or a grain of sand - this is the firewood of this world. The rules here are simple and straightforward: Every citizen is obliged to enter another world at least once and bring back as many items as possible. This is a world where everyone can summon familiars. But contracting a familiar comes with a price - if you contract one person, you will live ten years less, if you contract two people, you will live thirty years less. This should be common sense to everyone, but there is no price for Yi Tian's contract with the demon. But the question is... Why are other people's familiars in the form of shadow wolves, griffins, and machine giants, while every familiar I summon is in human form?