  We show that the modular branching rule (in the sense of Harish-Chandra) on
unipotent modules for finite unitary groups is piecewise described by
particular connected components of the crystal graph of well-chosen Fock
spaces, under favourable conditions. Besides, we give the combinatorial formula
to pass from one to the other in the case of modules arising from cuspidal
modules of defect 0. This partly proves a recent conjecture of Jacon and the
authors.
