For identical bosons interacting via a large s-wave scattering length,
Efimov states and their associated universal few-body bound states
appear. For fermions, in particular in a mass-imbalanced two-component
Fermi system with a large inter-species s-wave scattering length, even
richer universal few-body and many-body states are expected to appear
from the competition between a repulsion by the Pauli exclusion
principle and the attraction induced by the resonant interaction. I
first explain universal three-body and four-body physics in the
mass-imbalanced Fermi system, and how they evolve as the mass ratio and
the s-wave scattering length are varied. Then, I discuss how these
few-body knowledge can be applied to quantum many-body problems of the
mass-imbalanced Fermi system.