Now that you mention it, the ferry girl likes throwing coins too.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.Those copper coinsrepresent "Heaven, Earth and Man".
Heaven = The round shape
Earth = The square hole
Man = The name of the ruler, the year etc.
Futo, how are you feeling? Having fun?Hmm, I don't know.If her body breaks down, does that mean she'll become a vengeful spirit like me?...That's a shame.Well, at least she won't become vengeful.Yes! The time of my life!So basically, use a stick with "My Faith in Amitabha Buddha" written on it to hit a youkai and it'll hurt more.