While you were being dragged around by Koneko she suddenly got a call on a phone, which you presume she got from Rias or the Lucifer at one point yesterday. Koneko pulls out her phone and answers it, before giving a monotone "Yes?" into it. You can hear the faint mumbles coming from the phone but not the actual words coming from it, which is strange because your ears should be able to hear perfectly at that distance. You see Koneko adopt an annoyed face before again, in a monotone voice saying "Fine.". Koneko hangs up before looking at you with a serious face and saying "Go back to the room. If you aren't there when I get back you will be punished!"
The face Koneko gave you at that time scared you, so you obviously said that you would be back before she did. You decided that now was the time to look for Sona, as per her instructions. Thankfully, you saw her earlier as Koneko was dragging you, thank the maou. You go into the garden where you saw Sona sitting at the table, and arrive quickly due to your photographic memory.
You see Sona still sitting at the table you saw her at before, even though it's been about half an hour since you've been there. You walk up to Sona and see that she's sleeping, which seems unusual for a heiress to do in public, but whatever, she promised that she would save you. Once you get close enough, you start telling Sona quietly to wake up, as shouting could possibly alert your sister. When she doesn't respond, you move to poking her in the shoulder, causing her to become startled and look around, not unlike a sleeping beast that was awoken. Sona continues looking around frantically before laying eyes on you, before calming down "So, you were able to get away?"
"Um yeah.. Someone called my sister and she had to leave somewhere" You reply, the excitedness of being away from your sister already making you super excited.
"Yes, I tricked Rias into thinking that she and Koneko should do bonding exercises."
You giggle, thinking about Koneko's face as she's doing said "bonding exercises", since Koneko had never been one for social contact. You suddenly hear Sona speak up. "So, there's only one way I can free you from your sister's control, which is _______"
A: "- to be my slave rather then Koneko's. I'm a more important devil in the general societies eyes so they would rather I stay then she stays" (Less Freedom, and Sona's Peerage can also take advantage of you)
B"- to join my peerage, since a person can't be under more than one person and I'm more important to devil society. You also become stronger to defend yourself from your sister" (More Freedom, and stronger)
C "- to become my sisters slave. If I ask her to accept you she would, and devil society would have no choice but to accept her decision (Very well protected, but Serafall is much more "Forward" then Sona, which would probably still lead to molestation. Less then Koneko, but still molested)