he/she is in an advisory role so the pay is based on what is agreed upon in a contract as the consultant which could be very little or quite a lot (depends on how good his/her mananger is). also since the mangaka has all the rights to the characters, they are free to contract other companies to make figures, models, fanbooks, etc, which can make them a lot of money (depending on how much he/she goes after those items). so it's all contracts with the mangaka having the upper hand. i read somewhere that ichigo mashimaro's barasui lost out a lot since he didn't go after the other markets for his characters (probably why we don't see too much ichigo mashimaro goods) . btw, he doesn't have a manager.