Responses
Basically it's all about jelousy. He wanted to take down Yashiro because he was about to take the spot as Misumi's sucesor. Yashiro has always been more valued by Misumi. Hirata couldn't kill him directly so he instigated Ryuzaki to do it. When that didn't work he tried to frame him with the drugs selling, wich was not allowed by the group. And the whole stuff with the gouda group it's also Hirata moves against Yashiro. I hope this explain things.
I couldn't fully understand the reasons behind hiratas behavior. Can somebody explain why he did all this?