The word umu is another word for agreeing with someone, like the word "yes" or "absolutely" in a cut-er way.
Person 1: Im telling you, the people will love the maid costume!
Person 2: So you are curtain this plan will work?
Persson 1: Yes, Im positive. Let´s get to work!
Person 2: UMU!
by Weeberuu December 24, 2018