how to show I fit in with the department during faculty interview

The other answer has good advice. But for a job with a research component, I'd interpret it at least partly as "How does your research synergise with our own?".

Point out things that you could work together with existing staff on; areas in which you could help each other out, and things where the combination of your skills/knowledge and their skills/knowledge might combine to produce something bigger than the sum of its parts.

Similarly, but less clearly, on the teaching side you might be able to identify how you fill a gap in their existing areas of expertise.

It's possible that the question is really "What can you do to help our department achieve its goals?" To the extent that they're asking that question, you need to understand what it is that they want. You also need to let go of any preconceived notions that might have about "every college or university wants x, y, and z", because priorities really do vary. In answering this question, you need to explain how you can contribute to the goals of the department.

This can be tricky to analyze because the real objectives of the decision-makers may not have been stated or might not match their public statements. Furthermore, there may be conflict within the department or with higher levels of the administration about what the goals should be. It's important to realize that the hiring committee would probably not have brought you to campus for an interview if they didn't believe that you could somehow contribute to the department. ("Probably" is here to exclude the small chance that the interview is a sham because some other applicant has been preselected. If you're caught in that situation then your situation is hopeless.) Therefore, it's likely that something or a combination of things in your application attracted their interest. If you can figure out what that was, and can convince the interviewers that you will deliver that desired result, then you will have successfully answered the question.

If there is conflict within the department or between the department and the administration, then the "wrong" answer to this question could hurt your chances of getting the job.

There are other possible interpretations of the question.

For example, the question could be "How will you get along personally with other faculty in the department?" It seems silly to ask that question, and the interviewers can probably judge this more readily by observing your behavior during the interview.

Or, they might be getting at "Will you be happy working at our institution and living in this place, or will you be trying to find a better job as quickly as possible?" If you can say "I really want to work here because ..." and you aren't obviously lying, then that will go a long way towards answering this version of the question. On the other hand, if you answer "I want to turn this institution into the Harvard of southeastern Alabama", then that might not go over very well.