Well i think Tsaesci are opposite of dragon because like dragons the have Thu'um the Tsaesci have kiai. And then they are both immortal and they both devour things, dragons eat souls and i dont really know what Tsaesci eat exactly but they ate dragons and men, but we don't know if they ate their souls too. And then Dragons are like the children of Akatosh who is represented as a dragon and then the Tsaesci may be the children of Lorkhan who is a Serpent/Snake

Kiai is probably just the Tsaesci word for Thu'um (to my knowledge, both the dragon word "Thu'um" and japanese "kiai" translate to "Spirit Shout." I assume "eating the dragons" refers to Akaviri Dragonborn and eating men is vampirism, but it is a good call on the serpent/dragon-to-Lorkhan/Akatosh symbolism.

So while I don't think you're quite 100% right, it is food for thought.