The girl's name is Tomoko Kuroki, a character from Tanigawa Nico's "It's Not My Fault I'm Not Popular." The adventure begins with the girl thinking to herself inside of a mysterious place called "The Abyss of Faithlessness". For unkown reasons she is attacked by spirits and she is saved by one of four doors that suddenly open.
In a panic, she rushes into one of the doors and wakes up in a very strange room.
Soul of the Abyss is also a prequel to another forum adventure named Sequel of the Lonely Girl. Soul of the Abyss resumes a unkown amount of time after the time that Sequel of the Lonely Girl leaves off. Judging from where Sequel of the Lonely Girl left off, it appears as though the main character is in some kind of after life.
The adventure has a number of different things that are left up to the readers to figure out on their own.
The first and foremost oddity is the langauge. Tomoko Kuroki comes from a place on Earth called Japan. Yet in the adventure she can speak and fully understand all the characters she has met thus far.
Bethesda, the maker of the Elderscrolls Series does not reveal what exact language the people of various provinces are speaking; nor do they reveal how different ethnic groups communicate.
The second oddity is Tomoko's body. In "Watamote" Tomoko does not have anyvisible breasts in Watamote, yet she does have them in Soul of the Abyss. It is not know whether she is in a different body, or whether she had aged.
The third oddity is the time period. The adventure does not reveal the exact time, but the appearance of characters Sigrid and Dorthe implies that it is close to the time that the game Skyrim takes place in. In one of the more recent panels of the adventure, something flies over the heads of Sigrid and Tomoko while they are talking in the garden. Although Sigrid says that it was just a hawk, one may never know what it really was.