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The spin- $1/2$kagome Heisenberg antiferromagnets are believed to host exotic quantum entangled states. Recently, the reports of $1/9$magnetization plateau and magnetic oscillations in a kagome antiferromagnet ${\mathrm{YCu}}_3{\left(\mathrm{OH}\right)}_6{\mathrm{Br}}_2\left[{\text{Br}}_x{\left(\mathrm{OH}\right)}_{1-x}\right]$(YCOB) have made this material a promising candidate for experimentally realizing quantum spin liquid states. Here, we present measurements of the specific heat $C_p$in YCOB in high magnetic fields (up to 41.5 T) down to 0.46 K, and the $1/9$plateau feature has been confirmed. Moreover, the temperature dependence of $C_p/T$in the vicinity of $1/9$plateau region can be fitted by a linear in $T$term which indicates the presence of a Dirac spectrum, together with a constant term, which indicates a finite density of states contributed by other spinon Fermi surfaces. Surprisingly, the constant term is highly anisotropic in the direction of the magnetic field. Additionally, we observe a double-peak feature near 30 T above the $1/9$plateau which is another hallmark of fermionic excitations in the specific heat. This combination of gapless behavior and the double-peak structure strongly suggests that the $1/9$plateau in YCOB is nontrivial and hosts fermionic quasiparticles.