Those copper coins

represent "Heaven, Earth and Man".

As they have people's desires placed upon them and circulate for several decades, they naturally accumulate spiritual energy of their own.

It makes no difference to a human, but against a shikaisen, the damage might be more serious than you think.

So basically, use a stick with "My Faith in Amitabha Buddha" written on it to hit a youkai and it'll hurt more.

Now that you mention it, the ferry girl likes throwing coins too.

If her body breaks down, does that mean she'll become a vengeful spirit like me?

Hmm, I don't know.

Futo, how are you feeling? Having fun?

Yes! The time of my life!

Well, at least she won't become vengeful.

...That's a shame.