[Excessum]

I wouldn't be so sure about particularly Swedish music being popular among the majority of Japans population, however when i did research on Japans Metal scene, i came across a lot of bands that are noting some of Swedish metal performers as their major influences. And indeed if you listen to some them, you can hear quite a bit of similarities. Unfortunately i can not list any other examples besides Blood stain child right now... (since i am way too tired/lazy at this point to look through the list of bands i did research on)...
In the end, when looking at how small the heavy metal music scene is in Japan (in comparison to Europe, for example), i would not expect foreign heavy metal bands to gain much popularity in the mainstream crowd.

When it comes to other genres - as someone wrote before, i truly doubt that they are keen on Swedish music in particular and if some gains success, it's just another foreign band that sings in englishs to them... pretty much like it is all over the rest of this godlike-Swedish-heavy-metal unappreciative world... haha

P.S. In Flames we trust! \m/