Tipping for "Free Walking Tours"

I have several different questions regarding tipping guides for free tours.

We will be having a tour of Himeji Castle with a guide provided by Himeji Castle English Speaking Guide Group. Is it appropriate to tip, and if so, what would the recommended amount be?

Also, it is my understanding there are free walking tours in Osaka. The same question for that tour--is tipping recommended and appropriate amount?

Thank you

IMHO, gift ( not money) would be more appropriate for the occasion.
Many years ago, I handed money in an envelope to a private tour guide in Hokkaido, and he apologetically returned it. Hence, I always prepare gifts for a similar occasion.

I think the best gift for the guide is your pleasure. Most of the guides are retired person who want to do something helpful to other people.

Japan is sometimes recognized as tip-less country, but I think this is not true (I am a Japanese by the way). "Keep change" when you get off the taxi is rather welcomed. At least when I took short distance and hand 1000 yen and say "keep change" (of course in Japanese) I have never refused it. But it might be noted that I am an old person (young students might not better to do this).

But in this case you don't need to tip at all. Just smile, say "thank you" and show your pleasure.

It is often illegal for a person to accept money for a service the person provided without a license or qualification. So if the guide says it's free, there is a reason for it, and items and favors will be the ideal gift for these cases. Something small from your home country would be great. And it's totally alright if you don't give any gifts at all. The guide probably enjoys free cultural/language exchange.

The guide probably enjoys free cultural/language exchange.

I strongly agree with Uco.

I asked a volunteer guide at Hikone castle.
She accepted just 1000 yen as the transportation fee.

She did much effort though it was so humid day.

So I ask her to have matcha service with us at the old tea house,
she declined our suggestion politely.

I gave a Japanese sweet and a cold drink to her.

A small gift from your home country would be prefereable. In my experience and learning, giving money can be offensive - it needs to be in the right context and a free guide isn't the right context.
About the only time I have "tips" accepted are late-night taxis when the fare is small and I sometimes manage to give 1,000yen - basically the fare and change (as mentioned above).

As an example of what to bring, we are from the Washington DC area and handed our guide a postcard-sized photo of the Washington cherry trees in full bloom. You want the small gift to be lightweight and packable.