i assume the original owner, unless they just didn't 'abandon' her to begin with or so since someone asked to look for something in that area but wonder if it'll lead to a clash or another mutually beneficial alliance
Yeah! Something like that, but we haven't known yet why Sacchan betrays sensei. Some speculated that it's toxic relationship. But, that won't work here in this series
My wild guess is that the first target is his sister, and Milnollis is basically possessing her body to keep her alive in some manner, which is why she looks like her.