Miaya is a mysterious character, all this is currently known is that she is extremely shy and thus doesn't speak verbally. According to Aoi Asahina, she speaks only through her computer via Usami.

Usami is gentle and kind-hearted, but is also very naive and not very smart. While she is strict about rules and other things, it's very easy to trick or persuade her. All she wants is to foster love, friendship and good manners, emphasized in her catchphrase "love, love!". Because of this, she can come across as overly sweet and annoying. She encourages everyone to live in peace and strength their bonds with each other. She is very happy and proud when everyone gets along, and scolds them when they do bad and kindly asks them not to do it again.

Character Wiki for Miaya

Character Wiki for Usami/Monomi

Japanese Anime Voice Reference

English Voice Reference

Notes: Please read each line 2-3 times with no slate. The third line is the most important though as it's part of the actual dialogue you'll be speaking if you're cast.