[quote=SailorMoon]
Mizuki is gonna leave them and then the man is gonna kill the ones you left. :( It would actually be funny if he appeared in the hot springs and like, they had a water battle. omg make this happen.
[/quote]

She left them because she already told them there is someone watching. Yuki and Akane aren't aware of this. She thinks it's better to know and be prepared, rather than not knowing.

Ya know, the people in the hot spring will already know something is wrong since Asuka is all battle ready mode.

Plus, Mizuki isn't a fighter (yet) and believes the hot spring group can hold their own.