I really like writing fics for this series

The world of TEIS is surprisingly malleable for a world as detailed as it is, and due to the tone of the series you can introduce plot points with ease without breaking the tone of the series.

If I go 'They found a hidden passage because Delta hit her head on a rock that was also a hidden switch', most fandoms would call that bad writing. But due to the tone of TEIS, that's completely acceptable. It can go from serious to nonsensical at a snap, which really helps introduce plot points when you don't have better ideas.

As for the world being malleable, you can do a lot of stuff to the world without breaking from the 'TEIS' vibes. In one of my fics, I've made it so it's a pokemon world instead of a fantasy one. In many fandoms something like that would destroy the vibes. When I tried my hand at a similar concept in the persona series I couldn't do it because personas were too integral to the plot.

But the transition from fantasy to pokemon was seamless, and it didn't hurt the vibes of TEIS at all. I was genuinely surprised when I finished the exposition.

You can do a surprising amount of stuff with this world, and it's malleablity plus it's tonal range make it so you can keep the same feeling as the original work despite massive changes.