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In the two-flavor chiral limit, the chiral phase transition of QCD is expected to be continuous and in the $O(4)$ universality class. Its real-time dynamics is expected to fall into the dynamic universality class of Model G, i.e., the one of a Heisenberg antiferromagnet. At larger baryon chemical potential, the $O(4)$ line is expected to end in a tricritical point, beyond which the transition becomes first order. In contrast to the $O(4)$ line, at the tricritical point the specific heat diverges, which potentially affects the dynamic universality class. We supplement the equations of motion of Model G by an energy-like density, and study the resulting dynamic critical behavior using the real-time functional renormalization group. We find that the order parameter still satisfies the strong dynamic scaling of Model G, but the diffusion coefficient of the energy-like density vanishes as $D \sim \xi^{-\alpha_t/\nu_t}$ with $\alpha_t/\nu_t=1$. We discuss the similarity of the tricritical point in QCD to the tricritical point in superfluid $\mathrm{^3He}$–$\mathrm{^4He}$ mixtures.