Japanese Naturalization Requirement/Process

Well, what I wrote was my experience. My case worker didn`t mention any timeframe, and I signed no pledge. He did say that it was a requirement but that they understood that it might be difficult to do - and as we know, in Japanese, difficult can mean near-impossible. This was three years ago, and no follow-up so far.

This said, I will start the process to relinquish early next year.

I strongly suspect that step-children/half-siblings will need to be listed and documents submitted too, but have no such experience. Probably best to ask at the first interview, where they will tell you what is needed.

do they give writing and reading test?

You need to personally write a statement about why you want to naturalise in Japanese.

All of the various forms need to be written in Japanese, but someone else can do these. But if you can do these, it will impress.