If I have to choose without thinking to much, then it would be a single book so you can read it from start to finish in one go. While there are shows with similar concepts, I don't think they are that enticing given that you tend to like certain characters that are developed to then vanish. This is diminished in a show format given that people are not positioning themselves as the protagonist, so it can be given a bit of leeway.
You can see this concept in animated series with Death Parade, which was good, but it left a bad taste after Chiyuki also reincarnated. Mind you, it was basically at the end so it was done well, but still...
This feels very much like you are grasping at straws. Maybe you should think about it more.
The game is a visual novel. Removing the player's agency to pursue certain story paths wouldn't fundamentally change anything about the characters, their interactions, alter the baseline premise, or change that fact that the whole point is to help these people along their character arcs so that they can let go and move on successfully. Taking out the choices and making it a kinetic novel wouldn't change anything more than set in stone a 'canonical' order of events, not alter the events themselves (outside of Mina, Natalie, and the epilogues).
Also, people absolutely position themselves as the protagonist of the show all the time. It's so common we have titles and tropes to describe, things like 'Protagonist Centered-Morality' where an audience is inclined it ignore or overlook the problematic aspects of a character just because they are the protagonist. Look at
Breaking Bad. Walter White is a monster, but people still love him as a character, despite that from any other perspective he should be by all rights an antagonist. Audiences very frequently give a pass to protagonists and their actions that they wouldn't other characters,
that's why it's a trope. They have fun following along on his adventures and want to see what he does next, but rarely do they critically examine what self-inserting themselves into such characters potentially says about themselves; because that would be uncomfortable, and most people have zero interest in engaging with their media that critically.
If, judging by your first aside, your problem was that the love interests are transient, then your problems is with the very premise of the story. Changing the format isn't going to fix that. A novel would still have the cast exiting the stage after they completed their individual character arcs, because that's sorta the whole point of the premise. If you didn't like it because you actually just wanted to keep everyone around for a big harem ending, then just be honest that you don't like the premise, rather than trying to play it off as it being a flawed format or whatever. It's fine to not like a story for personal reasons, but that doesn't make it a bad story just because it wasn't offering what you wanted. There are legit criticisms you can level at
The Interim Domain, it not being a novel or animated series isn't one of them.
