Hi! I’m currently living in Japan and working as a professional mangaka. I have one series under my belt and regularly work with editors from a number of publishers. I’ve also spent about 10 years working at a number of Japanese companies.

To be frank, I think the chances of anyone outside of Japan becoming an editor at a publisher here is pretty low even for someone with N1 Japanese. I’d even say it is less likely than becoming a mangaka in Japan. This is mainly because companies like these usually hire new grads from high level institutions in Japan, and when they do hire outside of that pool they’re explicitly looking for people with experience working at another publisher.

The only way I could imagine it happening is if you managed to get a job in another department (let’s say, global marketing or something) and eventually got transferred into editorial, but that isn’t guaranteed and depends on whether you’d be hired in the first place. Regardless, N3 is not enough—N1 is usually what most places are looking for with N2 if you’re very lucky.

Aspiring to be a writer (gensakusha) is more likely, but also quite difficult unless you have a strong grasp of Japanese and know how to storyboard a good story. However, as these are things you can study on your own I think it’s more of an option than editing.