Hello everyone,
Sorry for the late reply, glad to see this has been of interest. Heard from our friend again today and he emailed a photo of the book. It is light pink with a marble-esque pattern and is pretty much the same dimensions as a Daily Text book. It is written in normal size font and in the vertical Japanese style. He asked me not to post the photo because he doesn't know how to remove "EXIF data". I don't even know what that is but will respect his wishes.
The only reason we can think as to why they went with the book of Matthew is that perhaps it contains the most JW friendly synopsis of Jesus life and ministry? I think Japan would be mostly Buddhist wouldn't it? Maybe Shinto? Not sure of the reasoning. My mate has recorded about 30 mins of the talk but is having trouble sending it on the hotel wifi. If it comes through I'll see if I can upload it. The talk was broken up with the speaker saying a few sentences, then a translator repeating what was said in Japanese.
With regards to the possible reasons for decline, one thing my mate has noticed there is that there are lots of sisters in the congregations and there were visibly more at the stadium for the talk. He was pretty happy about that LOL! It seems that there are lots of unbelieving husbands. So maybe what is happening is the kids of these families are now getting to an age where they can make a decision, and choose not to go down the JW path. There is huge pressure for kids to go to University in Japan, and my mate said that there is huge pressure, especially for the brothers to be pioneers, MSs, and elders. Pretty much if you aren't a pioneer, you aren't considered marriage material.
These might be contributing factors? Surely the internet mustbe playing a role.