As a recruiter of English language teachers, I would be looking for your motivations and I would be looking for a commitment from you that you are serious about moving to Japan.
Firstly, by simply completing the task for AEON you are demonstrating that you are a serious applicant so I wouldn't be too concerned about the content - by writing anything at all you've scored one point.
To score another point with the recruiter at AEON - check the document for errors. You are applying for a teaching post so they will be looking at how you communicate and they will expect perfect English.
Now onto the content itself. The key here is your motivations. You know your best students are the ones who are motivated. AEON is looking to reduce their risks when they recruit you. They want you to complete the contract. If you are genuinely interested in any aspect of Japanese culture it makes it more likely you will enjoy life in Japan and therefore reduces AEON's risk when they employ you.
Just be truthful - tell them what you love about Japan, tell them why you want to work there and what you expect from the placement. Again it reduces AEON's risk if they know that you know what you are committing too.
I've been in TEFL recruitment for 10 years and the last thing anyone wants is for a candidate to arrive and then say they hate it and want to leave. Recruiters will do anything to make sure this doesn't happen. AEON's application process will have this in mind and I'm sure that this is the main purpose of this essay...
Best of luck with it
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