  We study fermionic fields localized on topologically unstable domain walls
bounded by strings in a grand unified theory theoretical framework.
Particularly, we found that the localized fermionic degrees of freedom, which
are up and down quarks as long as charged leptons, are connected to three
independent N=2, $d=1$ supersymmetric quantum mechanics algebras. As we
demonstrate, these algebras can be combined to form higher order
representations of N=2, $d=1$ supersymmetry. Due to the uniform coupling of the
domain wall solutions to the down-quarks and leptons, we also show that a
higher order N=2, $d=1$ representation of the down-quark--lepton system is
invariant under a duality transformation between the couplings. In addition,
the two N=2, $d=1$ supersymmetries of the down-quark--lepton system, combine at
the coupling unification scale to an N=4, $d=1$ supersymmetry. Furthermore, we
present the various extra geometric and algebraic attributes that the fermionic
systems acquire, owing to the underlying N=2, $d=1$ algebras.
