The 220~PeV neutrino KM3-230213A, in tension with IceCube and Auger unless the underlying spectrum is narrow (a $\sim 2\sigma$ upward fluctuation in any case), admits a two-body reading: relic decay $X\to \nu \bar{\nu }$ with $m_X\approx 4.4\times {10}^8$~GeV. Consistency with neutrino and $\gamma$-ray bounds sets $\tau /f\approx {10}^{29}$–${10}^{30}$~s, lifetime over relic fraction. For a flavored ${}^1{S}_0$ onium, the operator scale lands in the Majorana-mass range of unified models: one Higgs insertion gives a singlet mediator, $\Mmed/|C_7|^{1/3} \approx 10^{14}$–${10}^{16}$~GeV across the allowed relic fraction; two give the seesaw window; Dirac or Majorana neutrinos select the branch. We give the construction and its decisive tests.