If it wasn't for migrants, would Western Europe have a lower crime rate than Japan?

No

Not at all. Japanese culture is way different.

Japanese people can be very violent. In fact, they have a huge problem with organized crime (Yakuza and other gangs) in their country, an element that is entirely absent from the societies of native North Western Europeans. Native Europeans are the most peaceful people.

Sure

no. Japan is one of the most law abiding societies on earth

Not necessarily. The Japanese culture is far more law-abiding and rule-respecting that western cultures.

Nope. If it wasn't for Americans, crime in the Western hemisphere would be a lot lower.