After looking up their backgrounds and the current anime plot, I’ve come to the conclusion that the ultimate mindscrew of this story will be that the person Nishina Toriko is looking for has never actually existed. I don’t mean to say that Toriko is crazy, as I do believe that she did indeed meet someone who called themselves Uruma Satsuki. However, I propose that the name Uruma Satsuki was an alias and not the real name of this person.
You all probably know exactly where I’m going with this. I believe Kamikoshi Sorawo is the “real” Uruma Satsuki. I came to this bizarre conclusion after reading her background information. A mysterious rival cult from the cult that her family joined literally tried to kidnap her repeatedly and everyone who could have known more details about Sorawo’s past are dead. My theory is that the mysterious gas leak that killed the cult that her family joined was set-up by the rival cult, who then successfully kidnapped her and brainwashed her into an alias to use her in order to discover more about the Otherside. From then on, as Uruma Satsuki, she cajoled the very lonely Nishina Toriko to join her after befriending Toriko and set out to search the Otherside more thoroughly for the cult. Whether due to guilt or realizing she had a double-life from her memories returning or due to some still unknown disagreement or fight with the religious cult that brainwashed her, she tried to escape from the cult by running into the Otherside after changing her appearance (i.e. cutting her hair, changing her clothes, etc) and lost her memories upon hitting one of the traps out of fear of the cult and recklessness as a result of that fear. Therefore, Uruma Satsuki is “dead” insofar as her alias was necessary to preserve her real identity. I say that Uruma Satsuki is the alias, because I doubt that Sorawo could realistically fake her ID for the college that she attends. Thus, Uruma Satsuki must be the fake name.
While the narrative has Sorawo feeling jealous or inadequate compared to this mystery woman, it stands to reason that there’s too many coincidences here and the fact a cult was literally trying to kidnap her in a mystery story with no one left alive to verify Sorawo’s life history suggests that it’ll be very important later. The narrative tries to position Toriko as the mystery girl, but we actually don’t know much of anything about Sorawo and the comparisons to Uruma Satsuki are suspect as a result. We’re told Sorawo looks exactly like Uruma Satsuki, but with shorter hair. Toriko feels comfortable as if she’s known Sorawo longer than three months. And we see that the Otherside can screw with people’s heads multiple times and change their personalities, such as every time Sorawo uses her eye power to gaze at Akari.
Unless this story gives clear specifics as to Uruma Satsuki’s background that demarcate her and Sorawo in some meaningful way, it seems likely that Sorawo herself is an amnesiac Uruma Satsuki.