  The isoscalar giant resonances for $^{86}\textrm{Ge}$ are studied by the
quasiparticle finite amplitude method based on the covariant density functional
theory. In addition to the well-known monopole-quadrupole coupling that splits
the isoscalar giant monopole resonance in axially deformed nuclei, a
monopole-quadrupole-hexadecupole coupling is identified in the triaxially
deformed nucleus $^{86}\textrm{Ge}$, leading to the emergence of a distinct
resonance peak at the low energy side of the isoscalar monopole strength
function. The transition density of the triaxiality induced resonance peak
shows a strong interplay among monopole, quadrupole, and hexadecupole
vibrations. The resonance peak responses to monopole, quadrupole, and
hexadecupole perturbations simultaneously, which could be regarded as a
fingerprint of the triaxiality in $^{86}\textrm{Ge}$.
