hi Yuji.
Welcome to this site.
I know your name in the site of toshimitsu (=domifara).
You write Japanese very well !
BTW, I'm answering to your question.
The table of holidays in pical_vars.phtml must be indexed 'Y-n-j'.
If you want to set every 12-25 from 1970 to 2030, you can achieve like this:
$this->holidays = array( ...
);
for( $y = 1970 ; $y <= 2030 ; $y ++ ) {
$this->holidays[ "{$y}-12-25" ] = 1 ;
}