He is a producer for GGC Production, and the producer of the popular Idol Unit AQUA. He often checks out the voice acting department to scout new talent. In actuality, he visits simply to check up on Senri and tries to convince him to join his newest production. However, after hearing Hime do the prince's role he becomes quite interested in scouting her as well. When she doesn't do very well at the one-line thug role he assigned her a few days later, he wonders if he misjudged her, only to be blown away in awe by her final attempt. He fires her, only to reveal that he has bigger plans for her in the future. Ever since then, he has planned to scout her for his own production as well. When he comes to scout a second time, after meeting Hime's mother and realizing that she thinks Hime's sister is more popular and important than Hime, and that Hime still continue to smile, so he promises her that he will help her accomplish her dream if she can do the same for him.
It isn't clear how Yamada knows Sakura Aoyama, but they have made a promise when Yamada was still in school. Their promise was when Yamada had raised a worthy voice actor, she would costart with the actor.
Yamada is Aqua's producer. He tasks Mizuki and Shuuma to look after Shiro's voice training and sometimes has them work together, like during the Aqua PV and Live.
Yamada met Hime at the Voice Over Academy during the Snow White showdown. He was interested in Hime's prince voice and wanted her to be a voice actor. Hime originally turned down the offer because she wanted to voice act for female characters. After having a dispute with Senri, she calls Yamada and says she will take any acting position. Despite her effort, he tells her it was no good. Really he wanted to use her for the promise he made to Sakura Aoyama.
After seeing her home life he yells at Hime's mother about how he will make her the best voice actor. He then makes her crossdress as Shiro and is told not to reveal her true identity understand any circumstance or she fired. He gives her an apartment and finds work for her until he completes his promise with Sakura.
It can only be asumed that Yamada continues working with her after she no longer dresses as Shiro.