For the last couple of years, I've been searching on and off for find a Japanese virtual assistant (a person who works remotely on a task basis) to help me out with my business. I finally managed to find one a couple of months ago, and thought I'd share some tips for anyone else looking for one.
Decide who you're looking for
The first thing to do is figure out what you need help with. For myself, the primary thing I was looking for was someone who could do first level Japanese customer support for Doorkeeper. I had been doing it myself, which had mixed results. On the one hand, some customers were glad they could talk directly to the founder. On the other, I'm not a native Japanese speaker (not even fully fluent), so composing responses was time consuming and they weren't even in proper Japanese (to the point sometimes people replied to my emails in English).
The person I was looking for obviously had to be a native Japanese speaker. I also wanted someone who could be regularly available, as opposed to in short bursts, so that replies went out to customers quickly. English comprehension was also important, as I'm much faster and accurate when communicating in English. Finally, I wanted to work with a single individual, as opposed to a team, as to do support independently, the assistant would need to become familiar with Doorkeeper itself.
Finding Japanese virtual assistants
Once you have an idea of what kind of person you're looking for, there are a number of different services that can help you find someone.
Kaori-san is a service specifically focused on bilingual Japanese virtual assistants. With the service, you pay a monthly fee for a certain number of "tasks" per month. This service seems great if you need help with tasks for everyday life, such as finding and booking restaurants. I haven't used it though, as I wanted to work directly with someone, whereas with Kaori-san, there is a pool of people who perform your tasks. If you don't have any Japanese ability, or your not looking to invest in building a relationship with a person, this could be a good option.
Gengo is not a virtual assistant service, but rather a translation platform. With it, you post translation jobs, and from their pool of screened translators, someone will complete it. There is no selection process, so you can view the service like artificial machine translation: put text in, a translation comes out (sometimes the translator will ask you questions though).
I tried them a couple of times, but found because translating a web application requires a high amount of context, we didn't have such great results. Because Gengo pays the translator per word, I don't think the incentives are aligned properly for something like translating a two word button, where a couple of paragraphs of text are required to describe the context.
On the other hand, if you have lots of content that can stand on its own, such as a product catalogue for an online shop, they could be a great option.
International Outsourcing Services
There are lots of popular international outsourcing services you can use to find a virtual assistant. However, we found that, at least in mid-2013 when we gave oDesk (one such service) a try, there wasn't much in the way of Japanese talent on the platform. Furthermore, the Japanese that were on it tended to be living abroad in places like the USA, which if you want someone to be available during normal working hours in Japan, doesn't match.
Domestic Outsourcing Services
In the last couple of years, there are several outsourcing services that have popped up: Crowdworks, Lancers, and Shufti are the ones I've heard of. The platforms themselves aren't as mature as their international counterparts, but they do have lots of Japanese talent on them. Most recently I tried Crowdworks, had about 20 replies to my posting within a day, and managed to find several good candidates.
All the domestic services only have Japanese user interfaces, so to use them, you'll need to at least have enough Japanese skills to navigate their user interface. However, I'd suggest making the job posting itself in English, as it will help you stand out among all the other postings and will attract bilingual candidates.
Evaluating a Candidate
Once you've found someone you want to work with, you need to evaluate them. In our case, we had most success with giving several promising candidates the same task. For instance, in our case, I sent a sample customer inquiry, gave some notes about what I thought should be included in the reply, and asked the candidate to draft a sample reply.
If a candidate didn't understand what you wanted them to do, disqualify them immediately, as likely their English abilities aren't good enough. Asking questions to clarify something is fine, but the candidate should be able to at least get the gist of what you want.
If you're having the assistant do something like translation or customer support, you'll also want to evaluate their Japanese skills. I've found that even if someone is a native Japanese speaker, if they haven't had previous customer support experience, they likely won't use the standard phrases used when replying to a customer (and Japanese culture values doing things in the standard way).
As a non-native speaker, it is basically impossible for me to evaluate someone's Japanese. I got around this by showing sample responses to several Japanese friends, and asking them which was best. Their feedback turned out to be invaluable, because the person I was initially leaning towards happened to be almost a native level English speaker, but didn't use the proper customer support expressions. Instead, I went with my second choice, who came up with a more natural reply, and has since turned out to be great.