Koyama and Shimanuki are a really fucking funny direction animation supervisor duo.
Like, I don't hate Masahiro Shimanuki as animation director, I find his style amusing, especially since it tends to make characters feel "potato"(like seriously, his hands are super super noticeable, he draws the most amazing sausage fingers), but at the same time, its definitely one of the most noticeable styles out of any animation director, and not necessarily in an absolutely "good" fashion. Its just incredibly noticeable.
And he is consistently paired up with, by far, the best regular episode director in the series, who is always hyper creative with all their storyboards.
Its just a really weird fucking duo, that somehow works? Like, all their episodes are absolute bangers even though because the direction is far better than it has any right to be. Among animation circles, its almost kind of a meme.
This is just my musings on the matter.