Riung is a umichooan woman who will have a huge impact in history.

The current version of Riung is a Keeper of the Umichooan Subtle Machine attached to the Umichooan embassy in Valtshora; she is mostly notable because of a lot of weird echoes travelling backwards in time from the future.

The moment that the time traveller Mariette Navia became aware of her presence she had a total meltdown; some versions of herself ran, others hid, and one decided to try to kill her with a huge sword and then freeze her in time.

On the other hand, at least one version of Riung from the future seems to find herself interacting with the Party:

Clark Dubois met Riung while while stoned out of his mind when captured by Victor Vituska's men. She mentioned never having met a Clark this young yet. In retrospect, Claire has concluded that Riung had never met her when she looked male.

Gaia Dynko met Riung when her attempt to learn dreamwalking went bad and she ended shooting an apparition of Vituska on the head in the middle of a hospital, resulting on the party being captured and jailed. Riung comforted her and gave her some counsel and a plate of supernaturally delicious cookies.

Maelle Kurimoto met Riung when they fell asleep after a very emotional goodbye to the version of Mariette who had tried to assassinate Present Riung; the Future One gave Maelle a hint so they could actually prevent the death of Mariette, for whom she apparently had not hard feelins despite the shanking.

Riung calls the place where she met Clark and Gaia “one of the White Sky Towers of Umichoo”: it is a tower big enough that visitors can't see the ground or ceiling when in the middle. It is also very white, and the walls seem to be inset with large round mirrors.

Riung has alluded to some kind of horrible catastrophe in her past… and probably the party's future.

But it is not the reason that Chronomancers are scared shitless of her; apparently that is the result of a “political kerfuffle” that will happen centuries down the line.

Riung was the first umichooan that the party met and she has, like other umichooans, features not found in our timeline. The best description that Clark could actually give was that she “looked asian”. Also ambiguously brown.

Riung's cookies are able to heal headaches, menstrual symptoms, and lack of sleep.

Mariette tried to explain that Riung is weird because she has a lot of inertia in time. At some point, it is very likely that almost every version of her will do some specific thing that will have huge consequences, but Mariette does not remember what.