  We present a $^{35}$Cl NMR study for spin $S=1/2$ perfect kagome
antiferromagnet Ca-kapellasite (CaCu$_{3}$(OH)$_{6}$Cl$_{2}\cdot$0.6H$_{2}$O)
with a magnetic transition at $T^{\ast}=7.2$ K. The static magnetic structure
in the ground state has been determined to be a chirality-ordered $Q=0$ state,
which is selected by a finite Dzyaloshinskii-Moriya interaction. The low-energy
magnetic excitations in the ordered state are investigated by the nuclear
spin-lattice relaxation rate measurement. We detect a weakly temperature
dependent contribution in the magnetic fluctuations perpendicular to the kagome
plane in addition to the dispersive spin-wave contribution in the kagome plane.
The low-energy magnetic excitations from the coplanar spin structure are
attributed to the zero mode originating from the flat band in this kagome
antiferromagnet.
