Calliope

UranianUmbra is an alien player from an unknown session of the game. Clues in the story currently suggest she is female, and a thirteenth troll player. She might be considered Jane's or Jake's patron troll, based on parallels between her initial conversation with Jane and Jake and other initial conversations of kids with their patron trolls. In particular, the HS 006081 (initial exchange) between UU and Jake is a near-perfect antithesis to the HS 002759 (initial exchange) between Karkat and Jade.

Her identity and whereabouts are as yet unknown. Her session of the game may be separate from all four known sessions (the kids' and trolls' pre-Scratch and post-Scratch sessions), but it is also possible she is one of the as yet unseen pre-Scratch troll players: the alternate-Universe versions of the trolls' Ancestors, who played the initial failed session. While the post-Scratch Handmaid or Condesce could be pretending to be her at the behest of Lord English, this is very unlikely as she would have to be lying to the point of character fabrication.

UU's associated symbol appears to be the caduceus (☤): a staff entwined by two serpents, which is usually crowned with wings. The caduceus is one of the symbols of the Greek god Hermes, the messenger of the other Olympian gods and also served as the patron guardian of boundaries and those who crossed them. Hermes' Roman counterpart Mercury is also associated with the caduceus, but he also served as the god of commerce and negotiation. In North America, the caduceus is commonly and mistakenly used as a symbol of the medical trade due to its similarity to the staff of the Greek god of healing and medicine Asclepius (⚕): a staff wrapped by a single serpent. When Asclepius died, his body became the constellation Ophiuchus, the Serpent Bearer. As the astronomical boundaries of Ophiuchus cross the ecliptic like the 12 signs of the Zodiac, Ophiuchus is sometimes included as the astrological 13th sign of the Zodiac.

If uranianUmbra is a 13th troll player of Sgrub and if her associated Zodiac sign is Ophiuchus, she might be located in the blue section of the hemospectrum between Vriska Serket and Equius Zahhak, akin to how the constellation Ophiuchus is between Scorpius and Sagittarius. Based on her chosen chat color and on the fact that Ophiuchus is rarely counted amongst the Zodiac, she may instead have a mutant blood color like Karkat Vantas or his his Ancestor. The additional constellation would also suggest some responsibility for bringing the kids' original session into existence, as her intercession also left a mark on the kids' universe, albeit a smaller one.

If UU is a pre-Scratch troll, she is likely The Dolorosa, Redglare, or Mindfang, since these were the female ancestors of Prospit dreamers. However, she could also be the pre-Scratch version of the Sufferer if his sex were changed, given that the caduceus is often linked to a myth concerning the prophet Tiresias who is said to have been transformed into a woman by Hera after he struck two mating snakes with his walking staff. The term "Uranian" is also linked to transgender/transexual concepts, as it is an archaic term used to define a third sex (originally only homosexuals, based on a character from Plato's Symposium who used the myth behind Aphrodite Urania to defend his mental and spiritual attraction to Socrates). The limited details on troll sexual physiology (e.g. both males and females in the post-Scratch session emit gametes of at least two kinds) leave the likelihood of such a change unclear. However, her text color is very similar to Karkat's: both are unusual choices of custom grays which differ slightly from the more common RGB-defined grays. In her color, the 6's from Karkat's color are replaced by 9's (#626262 becomes #929292), and Karkat's symbol is a sideways 69. Given that Jake is Jade's counterpart in the post-Scratch session, and the initial conversation between Karkat and Jade antithetically mirrors Jake's initial conversation with UU, this further suggests a potential relationship between UU and Karkat. If Karkat HS 5917 (gave the kids' universe cancer), UU (as a symbolic healer if associated with Ophiuchus) could possibly provide the cure.

Her HS 006081 (conversation with Jake) includes details of her alien family structure that are consistent with what is known of troll development. At the end of the HS 6013 ([S] ACT 6) flash, a terminal with her caduceus symbol can be seen. HS 6014 (The subsequent panel) shows a pair of troll-like hands, and the screen displays Alternian text that reads "Click ==> to continue." It is unknown if these hands belong to UU, as the terminal appears to be similar to the Homestuck Interface Devices used by Exiles, except with only one screen.

Trivia

 * UU has yet to reveal to Jane and Jake UU's real name, suggesting to Jane that it "it may be for the best that yoU never know it," because "it coUld stir Up some things best left in their present eqUilibriUm." This suggests her identity is of significance to Jane, and that she may be someone that a member of Jane's session has already met, or will meet in the future.
 * The 4 universes that UU refers to are: the instance of the trolls' universe in which the Ancestors played Sgrub (A1), the instance of the trolls' universe in which the current trolls played Sgrub (A2), the instance of our universe in which the pre-scratch kids played Sburb (B1) and the instance of our universe in which the post-scratch kids will play Sburb (B2).
 * Most likely, as the kids and trolls' pesterchum handles are combinations of the A, T, G and C bases of DNA, this troll's obsession with the letter U is a reference to uracil, a nucleotide base that RNA contains in place of thymine (T).
 * The astrological significance of the U may be a reference to the planet Uranus, or to one of the proposed zodiac symbols associated with Ophiuchus: a U with a tilde-like symbol superimposed across it, which is a stylized representation of a man carrying a snake. As Ophiuchus is not a zodiac sign, there is no standard Zodiac symbol associated with it, but the U symbol has gained popularity in Japan since its introduction in 1995. Ophiuchus is is the only constellation outside the Zodiac that physically crosses the Earth's ecliptic. As Zodiac signs only have a loose association with the actual location of constellations in the sky, the "duration" of Ophiuchus's effect on birth sign, if it were given a Zodiac sign, would be an entirely arbitrary assignment.
 * UU's text color is defined by the hex code #929292; 92 is the atomic number of uranium.
 * An umbra is the darkest part of a shadow.
 * The beginning of UU's HS 6044 (conversation with Jane Crocker) is a direct parallel to Karkat's HS 2759 (CONVERSATION WITH JADE) which was revealed to be about her prototyping of Bec. HS 4039 (This Aradia-Kanaya conversation) also parallels that conversation.
 * UU's client begins and ends with cheering, which is different from Trollian, Pesterchum and Bettybother which begin and cease with Trolling, Pestering and Bothering for each of its respective clients.
 * UU is the only character that uses British spelling, such as the characteristic U in certain words.