It would depend both on what he wants to do, and what you mean by 'graphics company'.
You would normally go about marketing your work the same way you would if you were making cartoons for a western-style cartoon (if his work is animated, i.e. Anime) or a traditional comic book (if his images are meant to be static, i.e. Manga). There is also the option of putting it all together into a portfolio and using it to get a job as an illustrator or animator with the many companies that produce such work for television, movies, and print.
As far as single images, I'm not sure. The anime 'style' is very popular, and, frankly, pretty easy to imitate. The true gruntwork is being able to do create the same characters from multiple angles, and progress them through a manga or animated sequence keeping their persona intanct. I would never, ever advise anyone just to send still images of their work out to businesses looking for buyers. He might well end up seeing a very similar character someday, without any credit to him. He should be a part of the production of the work he has created, and not just sell the rights to an image.
Has he put together stories of his own yet? If not, I would advise him to begin to do storyboards, plotting his story and carrying the characters he has drawn through it. It is a huge industry, and I am sure that with practice he could do very well.