  Amaterasu, the second most energetic ($244$ EeV) cosmic ray particle has been
recently detected by the Telescope Array (TA) surface detector. The origin of
the TA Amaterasu event is puzzling, as its arrival direction points back to a
void in the local Universe, lacking conventional astrophysical
ultra-high-energy (UHE) cosmic ray (CR) sources. Hence, we explore the
possibility if this TA Amaterasu event could have originated from the decay of
superheavy dark matter (SHDM) in the Milky Way. Such an origin also opens up
multi-messenger detection channels in both UHE gamma-rays and UHE neutrinos. In
this present work, using the TA Amaterasu event and the multi-messenger
limits/sensitivities from various UHE telescopes, we place stringent
constraints on the lifetime and mass of the SHDM. We find that the
non-detection of the corresponding gamma-rays at the Pierre Auger Observatory
(PAO) and the TA is in severe tension with the SHDM parameter space required to
explain the TA Amaterasu event. Additionally, we extend the multi-messenger
analysis to the future UHE gamma-ray and UHE neutrino telescopes such as PAO
upgrade, GRAND 200k and IceCube-Gen2. We find that the bounds from the future
neutrino telescopes will be able to compete with the present UHECR bounds.
However, compared to the existing UHE gamma-ray bounds, the future PAO upgrade
and the GRAND 200k gamma-ray detectors will improve the bounds on SHDM lifetime
by at least one order of magnitude.
