Maribel is a student on the outside world, presumably in a college or university. She majors in relative psychology and sometimes has difficulty telling the difference between dream and reality. She believes subjectivity to be more true than objectivity. Together with her friend, Renko Usami, she has an interest in what would be considered the paranormal. Their club, consisting of only the two of them, describes itself as a club for necromancers. However, they don't do many of the things necromancers would normally be associated with. Instead, they investigate spirits and such. Specifically they're interested in Gensokyo and seem to be among the few, or even the only, humans on the outside world who know of Gensokyo's existence. Maribel has visited Gensokyo in her dreams.
Due to both characters having boundary-related abilities, as well as a degree of visual resemblance, fan theories abound about a possible connection between Maribel and Yakumo Yukari, with some even going so far as to suggest that they are somehow the same person.