After the quincy invasion, the soul society was in ruin. Yamamoto was gone and the gotei 13 has't been this low for a while. And the higher ups of the seireitei aren't helping with their decisions which contradict's Shunsui so they with their lieutenants come forward but since you are the protector of the higher ups you stop them.

Shunsui: Move aside this doesn't involve you

Shunsui said, his flamboyant and playful mood over as Byakuya and the other 11 captains come forward

But who are you? You are an ancient shinigami at the same time as the original gotei 13 and you were picked for the guardianship of the higher ups. Basically you are the loyal dog for them. You are considered Admiral and even the squad 0 know about you and you are very well known around soul society but no one truly knows who you are.