It's certainly one of the most playful dom/sub relationships I've seen here. While she will help you in everyday situations like doing the chores or seducing your mother, the facade of "bad sister terrorizing little bro" stands and she's not a "public slave" or similar. Also from the sauna first fucking scene I gathered that she does not really see herself as an inferior, like many subs do. And yes, I like that a lot over the more extreme and silly variations of "parading naked in public with a leash" (which can also be entertaining if done right, don't get me wrong, but just wouldn't work in this more realistic setting IMO). In the end, she still has a personality.