How do you answer 'Where do you see yourself in five years' if your plan has no relation to this job?

When an employer asks this question, they are really asking two separate questions:

1) Do you have goals/dreams/aspirations?

2) Are your goals/dreams/aspirations in line with this company?

With that in mind, you need to decide what about this job IS relevant to your 5-year plan and communicate it.

I would explain how I plan to use this job as a rung in the ladder to other achievements.

By asking this question, employers are basically filtering those employees who have a clear mindset about what they wish to accomplish and by what means i.e a career plan in order to achieve career goals and objective. this question by saying something like " I see myself progressing in my field as well as in the company and learning new skills to the benefit of the company. I believe this job will be very challenging and motivating. I can see many challenges ahead and therefore, I am willing to invest my time learning all aspects of the job towards professional advancement. "