  In this work we consider a fermionic chain of finite length $\ell$. Fermions
are allowed to interact and are forced to obey boundary conditions, thus
altering the process of condensation. Our goal is to explore how this affects
the quantum vacuum energy for this system. We approach this problem by using a
self-consistent method and observe a nontrivial behavior in the Casimir force,
displaying a switch from an attractive to a repulsive regime. This flip stems
from the competition between the attractive contribution from the usual
fermionic Casimir effect and a repulsive one coming from the condensate.
