1) Japanese companies don't buy SaaS.
2) Japanese companies do buy software, but it is overwhelmingly sold through existing commercial relationships they have with individual salesmen, even for packaged software. This is not an easy sales channel to just show up in one day. (I am not exaggerating the following anecdote in the slightest degree: my manager needed to invite a salesman out to drinks for us to procure a license of MS Office at my old day job.)
3) Japanese: occasionally tricky.
4) The problem domain for Japanese invoicing: potentially tricky, if you weren't expecting things like "We need photographic reproductions of the company seal on all our invoices. Naturally." to be hard requirements.
5) There's a sentiment among some members of Japanese society, including occasionally ones who have input in purchasing decisions, that you can only possibly understand Japanese language/culture/business practices if you are Japanese, and therefore, if you are not Japanese, they might not be overwhelmingly predisposed to doing business with you.