This is first and foremost a Buddhist themed object. Are you sure it's Japanese and not Chinese? The Yin and Yang symbol coupled with the pig makes me think this is Chinese, though the symbols can be from either culture as both adopted Buhddhist traditions and used their symbols in their art.
The pig may have been used as a representation of the Year of The Pig, perhapse when this piece was manufactured (but since this year repeats every 12 years it's impossible to say which year in our calendar it represents specifically).
The pig looking into the drink also reminds me of Zhu Bajie, a character from the widely popular 16th century Chinese novel Journey to the West, he is a man who takes on the form of a pig due in part to his heavy drinking. It's probably not related but it reminds me of that. That story is centered on the Buddhist tradition as well.