Looking past to semi-obvious Celtic/Viking elements, let’s consider the three people in the above image: Who are they? The person in white – a lone defender? A lone survivor? A conquering wizard? The poor, unlucky bastard sent out as bait for parlay? The greeter, welcoming the arrivals to the afterlife?
Likewise the arrivals on the left: Returning home? Lost travelers, seeking shelter? The (likewise) poor souls sent as bait for parlay? Recently departed warriors arriving at the next spiritual plane.
I like that one… Let’s consider the afterlife idea for a moment… what if they don’t want to be there – they want to return? What if it’s not where they were supposed to go…maybe they were pulled to another space, recruited for something. Are they the first to be selected? The ones that finally succeed…or that see through the plans to something else. Are these two people clansmen/somehow positively connected, or were the opponents in life, possibly responsible for each others deathblows. What if the (potentially nefarious) plans involve pitting the two against each other, maybe until they discover the shadiness, and grudgingly start working together…
Now, what if it’s not so much an “afterlife” but a dimensional shift…not necessarily vikings, but alien species. A “First Contact” or “Testing Humanity/[Other Species]” scenario, perhaps? Or something else entirely?