A kid and his dog cross a frozen mountain in a blizzard with nothing but stubbornness and survival instinct. The animation holds still when it matters most, not wasting motion on the easy moments, then breaking into desperate, scrappy action when the cold actually starts winning. This is the kind of OVA that respects both the landscape and the kid's smallness against it, builds real tension from nothing but snow and time, then ends before it overstays. You don't get many one-shot stories that nail this: quiet dread, then earned relief, then done.
Kakkoii 1-nensei: Yuki no Bouken is a action OVA.