Mayuri is Okarin's childhood friend and lab member 002. She has romantic feelings for Okarin (in some timelines they are pursued) but Okarin sees her as a younger sister he has to protect. She is very ditzy and naive but really sees Okarin and when he changes better than anyone. She has her own way of supporting him and tries her best no matter what. The biggest thing acting wise about her is she kind of keeps her upbeat attitude even in hard situations. 

Here is a link to the tutturu!! It's very well known across us Steins Gate otaku's

 https://www.youtube.com/watch?v=xesBMtbaVQI&ab_channel=EpicIn