It is entirely possible that Unit Chi is actually a lovely, more-or-less sane person. Unfortunately it's very hard to tell underneath the fundamentally broken world-view obtained by believing what she is told by the other Explorators, who are all utterly insane. Chi is gullible, well-meaning, curious, attentive and easily frightened. She enjoys being useful, making cake, and interacting with machines. She also believes that the trees are trying to murder her, that food should be homogeneous, that the removal of important brain functions is a good solution to most problems, that Unit Delta is a good person to have poking around in your insides, that emotions are terribly bad for you, and that THERE IS NO DECK THIRTEEN.
Despite being a very competent mechanic, Chi has become somewhat accustomed to using her MIU for everything, and as such is inclined to have some difficulties adjusting to aspects of the environment that she can't plug herself into. She finds written information mildly irritating because of how inefficient it is as a means of communication.
Her memories don't extend back very far. They certainly don't cover any time before she met the Explorators. Those memories have been removed for her own benefit, which she knows because Unit Delta has told her so. It remains unclear whether she was ever actually assigned to the Explorators, or whether she was just straight-up kidnapped and brainwashed.