Consider this - most jobs you won't be going more than 2km, if that. What bike you ride and how fast you are is not going to matter so much, how well you do in an interview and how well you understand Japanese is going to be vastly more important, and there is no special vocab to understand, its "take this to Mr A in Building B".
You underestimate the importance of language skills even more than the OP did.
When I decided to try to get a job driving trucks, I was extremely anxious worrying if my Japanese was going to be good enough. A couple of years later, things were going well enough with me that my company decided to take a chance on another foreigner, a Tunisian. Unfortunately, his take was exactly the opposite of mine. His idea was, "My Japanese isn't very good, so something like this is all I can do." Nothing could have been more profoundly mistaken.
My job even today requires very little verbal interaction...probably not more than two minutes a day, on average. But just because there is little of it doesn't mean that I can get by with a half-assed grasp of the language. You have to keep in mind that what I do, and what the bike messengers do, is unique in that we take very valuable items entrusted to us by the customers and then move them around
unsupervised. That means anything that comes up, you'd damned well better have the language/cultural skills to straighten it out and do it on your own. He'll have to deal with the company environment at work, talking probably quite extensively over the phone each day, both to dispatch and to customers, and he'll have to have good reading skills as well. He's going to have to do a good job of selling himself, largely based on personality and language skills, or he's never going to make it past the interview stage anyway. Being able to comprehend just simple "Take this from Point A to Point B" sentences is
not going to cut it.
The largest potential problem, I suspect, will be that employers will not want him based on being a foreigner....and that will be because they will assume, rightly or wrongly, that some or all of their clients would balk at turning over valuable packages to him. And when I say "valuable packages", that is precisely what I mean. Japanese securities laws require that stocks/bonds traded actually physically change hands at the end of the trading day. They can't do like in some other countries and just keep an updated log of who actually owns what. Bicycles haul securities back and forth between brokerage houses, which tend to be geographically concentrated (making bicycles practical).
Something like what you have would be suitable I guess.
