This is a one-shot that swings harder than it has any right to, building a whole world of lunar corruption and border village collapse in minutes and asking who steps in when nobody else can. The language itself is archaic and grand, "Whomst defends the world's justice?", but it's not pretentious; it matches the scope of what's actually happening, fiendlings overrunning the weak while asking the question every hero story needs to answer first. By the time you reach the end, you've felt the weight of a fallen moon and understand exactly why someone has to become the vileslayer.

A tyrannical moon hangs over border villages as fiendlings surge out from beneath a vast silver sea. The weak are drowned out by sinister laughter until only sorrowful sighs remain. Then the people look to the sky and find their answer in falling stars: the Ninja Heroes who keep watch among the stars arrive, carrying a dazzling otherworldly fire meant to wipe out the calamities besetting the land. Their arrival is cast as divine retribution in the Mappou Age. The result is a single-episode ONA blending action, fantasy and sci-fi.