Higher score purely for the fun of the concept: A reverse Isekai giving the idea that our peaceful world is the one heroes would want to spend time in. Now this is an OVA, and it certainly feels like an OVA in every sense. Without reading the original novel myself, I can tell this animation attempts to nod to audiences that read the novelization and includes the characters from it. Still, I believe the characters have some charm to them even as the episode seems to expect you already know them. The story does a decent job of moving fast by using comedy and then addressingcharacterization with interactions, considering how limited their time was. It captures some of the feel of the concept while focusing mainly on a character's adjustment and development. Although not the most relatable, I found the character's unique hang up to be fun to address, and I think it was described just well enough to see why she acts the way she does.
I'm not the most attentive to art or sound, but I did enjoy the designs of the characters and the animation, and the sound never stood out as out of place to me.
Because of how much fun you can get out of a single episode bringing the concept to life, I do think "Eiyuu" Kaitai is worth a watch.