  The largest solar flare have been recorded in gamma flash and hard spectra up
to tens GeV energy. The present building and upgrade of Hyper- Kamiokande (HK)
in Japan and Korea, (as well as Deep Core, PINGU) Megatons neutrino detectors
do offer a novel way to detectable trace of solar flares: their sudden
anti-neutrino (or neutrino) imprint made by proton scattering and pion decays
via Delta resonance production on solar corona foot-point. These signals might
be observable at largest flare by HK via soft spectra up to tens-hundred MeV
energy and by IceCube-PINGU at higher, GeVs energies. We show the expected rate
of signals for the most powerful solar flare occurred in recent decades
extrapolated for future Megaton detectors. The neutrino solar flare detection
with its prompt alarm system may alert astronauts on space journey allowing
them to hide themselves into inner rocket container surrounded by fuel or water
supply. These container walls are able to defend astronauts from the main
lethal (the dominant soft component) radiation wind due to such largest solar
flares.
