Why does Eimu wear a different uniform?
Much like this question, this is most likely to be part of the Transfer Student Uniform trope that features in a few anime.

TVTropes page


  New Transfer Students in places where school uniforms are a cultural default setting often wear their old ones until the school can provide them with a new one. In fiction, this shows the newcomer or outsider. When they get the current school uniform, this indicates they've been assimilated. If the student is meant to be a Fish out of Water, they will keep their old uniform throughout the series. In Japanese media, even rebels don't choose to abandon uniforms entirely; in American media they will do this even if the new school doesn't have uniforms. Compare the Non-Uniform Uniform.


Thanks to @Jon_Lin