A corset really keeps boobs well in place. You really have to move them quite a lot to have them out without untiying the corset
Regarding Sheryl's problem... V-type infection. My hard working brain tells me that V stands for Vajra... does it?
And for some reason the quartz she wears has the infection quiet. She probably needs both for the infection to be totally quiet. One is missing, she gets symptoms.
Following this idea, yes she needs to team with Ranka that will have some kind of control over the symbiosis Sheryl needs to have with the infection.
Regarding klan, she mentionned the fact that in her zentran form she could be of some appeal to Mickael. Well just do it