Ainz and Cid swap bodies and neither their subordinates nor their enemies notice the difference, which means watching two overpowered protagonists fumble through each other's absurd power hierarchies while keeping up the act. The comedy lands because it treats the premise seriously enough that the fish-out-of-water moment actually stings, a skeleton trying to be an edgelord assassin, a shadow operative trying to monologue like an undead overlord. This is the crossover that only works if you've watched both shows, which is exactly the point; it's built for the people who already know why this swap is the funniest possible thing these two franchises could do to each other.

Ainz and Shadow have swapped bodies for reasons that are never quite pinned down, and somehow nobody around them has picked up on the switch. Their masters may have traded places, but everyone carries on as if nothing is different. The short comedy fantasy ONA is a Halloween crossover between Overlord and The Eminence in Shadow, with both casts drawn in chibi form. The humor rests on the swap going completely unnoticed.