The Monkeys In The Z-Drive.

One of the many details that I like, noticed upon a first watch but it is only really beginning to hit me...the monkeys in the Z-Drive have exactly nothing to do with AU Powder.

Like she gives a very clear curious look when he is making them, and for good reason. To AU Powder, these are just toys she tinkered with as a kid. They likely hold even less significance to Ekko, as far as she is aware. We don't see her useing this in any of her doodles (as usual, I'll add here as far as I remember and feel free to tell me in the comments if I am wrong XD). It's not as meaningful to her.

But MU Jinx has taken them on as not only a calling card, but as one of her go-to weapon forms.

And Ekko makes a bunch of them and puts them into this device. For his Jinx. Because they mean something to her.

EDIT: I was SO very wrong about this. Genueinely astounded by many people seemed to like this with me being so wrong.

To explain: AU Powder DOES use monkeys, we see one fall in her shop at one point. So this kinda doesn't hold water anymore with that fact being true. Which sucks but, still.