Second, the personality of Diligent. This was a tough one and a compromise from the beginning. The use of "Dear Guest/Customer" and offering to be of service in the dialogue tends to make me lean toward asdfqwertyasdf's interpretation of Staff. It may not be even close to the original name/translation but is a much better fit.
I'm going to suggest: Service Staff or asdfqwertyasdf's shortened Staff
They didn't elaborate too much on it but... this place is a brothel. All the girls are part of the staff, actually.
Most of them are offering the "girlfriend experience" type of service, while the diligent one use proper etiquette when it comes to commerce and service, and thus address you like any Japanese employee would address a customer.
It says a lot about that girl personality : even though she works in a house that specialises into intimate experiences that mimic real relationships, she's so obsequious and conscientious about her duty that she can't help but treat you like a proper customer should be.
In this context, I believe that "Diligent" does a really good job at conveying her personality. While "Staff" is a little bit more explicit about her behaviour, it doesn't have the same nuance.
Might I suggest that instead of "Diligent" or even "Staff" perhaps the term "Proper" would be more fitting. If someone is always well mannered and uses proper etiquette then in the West that person would be called "proper", as in the oft-used term "prim and proper".
Other terms that may better fit that I might suggest is;
"Decorous"
In keeping with good taste and propriety; polite and restrained:
From the term "Decorum" - behaviour in keeping with good taste and propriety.
synonyms: proper, seemly, decent, becoming, befitting, tasteful, in good taste; tactful, correct, appropriate, suitable, fitting, fit; polite, well mannered, well behaved, genteel, refined, polished, well bred, dignified, respectable, courtly, civilized; formal, reserved, modest, demure, sedate, staid, gentlemanly, ladylike
Or even
"Courteous"
polite, respectful, or considerate in manner.
synonyms: polite, well mannered, civil, respectful, deferential, well behaved, well bred; gentlemanly, chivalrous, gallant; ladylike, genteel; cultivated, gracious, obliging, kind, considerate, pleasant, cordial, genial, affable, thoughtful, urbane, well brought up, well spoken; formal, proper, polished, refined, decorous, courtly, civilized, tactful, discreet, diplomatic;
I feel those three terms align much better to her personality than "Diligent" or "Staff" does.
