お題箱からです
ユーミルと誰かで衣装交換でしたが、雪解けの季節なのでニフルにしました 捏造
ありがとうございました！

From the suggestion box
It was supposed to be a costume swap between Ymir and someone else, but as it's the thawing season, I went with Nifl instead. Just making it up as I go.
Thank you very much!