Manami is a surly teen who places importance upon logic above all else. She often looks down on others as overly emotional or consumed by their own problems. She comes off as apathetic and rude in most circumstances.
Despite being unable to swim, Manami has obtained the mysterious ability to breathe underwater. She hates this, but finds it necessary to use it so she can explore the ship she finds herself upon. It may also be possible for her to manipulate water, but she doesn't explore the possibilities more than needed.
Manami wants to go home simply because she finds where she is generally unpleasant. There is little indication she would be much happier at home, but it's a better goal for her than standing around. She assumes there is a logical explaination for how she got into this place.