  We discuss the codimension-1 defects of (2+1)D bosonic topological phases,
where the defects can support fermionic degrees of freedom. We refer to such
defects as fermionic defects, and introduce a certain subclass of invertible
fermionic defects called "gauged Gu-Wen SPT defects" that can shift
self-statistics of anyons. We derive a canonical form of a general fermionic
invertible defect, in terms of the fusion of a gauged Gu-Wen SPT defect and a
bosonic invertible defect decoupled from fermions on the defect. We then derive
the fusion rule of generic invertible fermionic defects. The gauged Gu-Wen SPT
defects give rise to interesting logical gates of stabilizer codes in the
presence of additional ancilla fermions. For example, we find a realization of
the CZ logical gate on the (2+1)D $\mathbb{Z}_2$ toric code stacked with a
(2+1)D ancilla trivial atomic insulator, which is implemented by a finite depth
circuit. We also investigate a gapped fermionic interface between (2+1)D
bosonic topological phases realized on the boundary of the (3+1)D Walker-Wang
model. In that case, the gapped interface can shift the chiral central charge
of the (2+1)D phase. Among these fermionic interfaces, we study an interesting
example where the (3+1)D phase has a spatial reflection symmetry, and the
fermionic interface is supported on a reflection plane that interpolates a
(2+1)D surface topological order and its orientation-reversal. We construct a
(3+1)D exactly solvable Hamiltonian realizing this setup, and find that the
model generates the $\mathbb{Z}_8$ classification of the (3+1)D invertible
phase with spatial reflection symmetry and fermion parity on the reflection
plane. We make contact with an effective field theory, known in literature as
the exotic invertible phase with spacetime higher-group symmetry.
