How is this related to Ukraine...?

According to the artist, the instrument at her right foot is a bandura and the weapon at her left is some Ukrainian version of a bardiche (I think, based on ベルベージュ). Also, it's named "Ukrainian Native Dress", where "X Native Dress" was an art meme on Pixiv a while back, but it's not clear whether this is actually native dress or not.

She is "Andriy Yuu Ceska", Naotan's original character. (the girl on the right of post #248622) She is half Japanese and half Ukrainian. [Source]

The artist played a trick on naotan.