Not sure why it would be anything other than the native S. foetidus, which is common in wet areas throughout much of New Jersey. And no, it’s not native to Japan.

There are 3 other Symplocarpus species in different parts of Japan, but this one looks like our native S. foetidus. I'm not sure what those 3 Asian species look like. You must have a seep or moist area if that's growing in your yard.