  We investigate the admittance of a metallic quantum RC circuit with a spinful
single-channel lead or equally with two conducting spin-polarized channels, in
which Majorana fermions play a crucial role in the charge dynamics. We address
how the two-channel Kondo physics and its emergent Majoranas arise. The
existence of a single unscreened Majorana mode results in non-Fermi-liquid
features and we determine the universal crossover function describing the
Fermi-liquid to non-Fermi-liquid region. Remarkably, the same universal form
emerges both at weak transmission and large transmission. We find that the
charge relaxation resistance strongly increases in the non-Fermi-liquid realm.
Our findings can be measured using current technology assuming a large cavity.
