As you appear in the Empty Sekai, you can see both Mizuki and Miku talking, but once they both notice you, the pink-haired girl quickly comesovef to you and greets you.

Hello, there! My name's Mizuki Akiyama. And this is Miku. She says, pointing at the girl as she hides her face.

She giggles at this as she looks back t you. Don't worry about her. She's just shy, but she'll warm up to you eventually! Mizuki's tone is rather upbeat and lively despite the place being grey and dark.