Uniform
noun
If you control people, you make them wear the same clothes. That's a uniform.
せいふく
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
アヤに、制服を着た女の子の絵を、立体派の画風を取り込みながら描いてもらいたいんだよね。
I want Aya to draw girls in school uniforms and integrate cubism style into it.