TV-Nihon

First we have to acknowledge that the bad guys get their name as a portmanteau of Yodomu and Jodunheim.

Yodomu 淀む/澱む 【よどむ】 (v5m) to stagnate, to be stagnant, to settle, to deposit, to be sedimented, to be precipitated, to hesitate, to be sluggish, to stammer, to stumble, to falter

I got the idea from this video:
https://youtu.be/7FZiAi9LDIs?t=709

It talks briefly about Japanese beliefs that flowing water is a sign of cleanliness and healthiness. That's why people stand under waterfalls to purify themselves.

Whereas water that doesn't flow (like the ones in the bad guy place) becomes stagnate (hey, that's the first definition of Yodomu). The water for them is dark and corrupting.

Maybe I'm totally wrong, but I think this is the best explanation that you're going to get for why there's just a bunch of water for the Jodunheim guys.

Every time I see it, I wonder what the actors feel having to shoot those scenes being in the water all the time.

i thought it was a norse connection of some sort since those words sounded familiar from the Thor MCU series.
so by this idea, does that mean the Jamental, the enemy version of Kiramental, come from not achieving ones goals and being stagnate?

Huh. Well as someone who has absolutely no knowledge of the Japanese language, that makes sense to me.

Do you know who's a perfect comparison? Murky Dismal from Rainbow Brite. He hates colors, and is trying to turn everything into a monochromatic drab world. If stagnation never makes it into the show, I'm hoping the word Murky does at least