In regards to current and future quests, I think that first of all, Nadia needs a more intense course in humility. She needs to realize that the more she looks down her nose and derisively dismisses those she considers to be beneath her; the harder and more difficult her own work will be... she's learned the completely wrong lesson from what happened two decades ago.... IF she truly wants to correct what she believes to be her mistake from back then she must be made to realize that it will have to be a TEAM effort with everyone on Dikadia working together for a common goal, NOT with her working by herself and erroneously dismissing everyone else as unsuitable or only worth something as test subjects in her fruitless experiments.
As for Zero, she also needs a similar, yet slightly different course of redemption... she needs to see that everything The Organization has told her all of her life is no more than self-serving, contradictory lies so that The Organization's Leaders can co-opt the entire power of the Island (and therefore the entire world) for themselves, regardless of the consequences for anyone else. To that end and to shake up Nadia, it might be a good idea to put Zero, Nadia and Jeanne in a monitored room telling them that they can't leave until they've sorted everything out between the three of them.... naturally, none of them would be allowed anything that could be used as a weapon. It would also be a good idea to have MC there as a moderator for a couple of reasons. First, to make sure things don't get too far out of hand and keep the discussion civil. Second, so that MC can get more of the answers he's been looking for, needing and deserves. It's my feeling that, in order for all of this to come Full Circle as it were, MC will need as much information regarding what happened 20 years ago as he can get, not only to fill in the gaps in his memory but to also help him master and control the powers that he has.
Thinking back to the situation with Nadia, it would also be good for her and MC to have a very long and serious heart-to-heart talk about absolutely everything that happened back then.... he NEEDS the answers she has and she needs to make more than a few confessions regarding her actions back then in order to relieve the overwhelmingly crushing guilt she's been living with ever since... about the only way that can happen is if she comes totally clean with MC.
The quest of Sarah's friend coming to Dikadia will have to answer a few questions right at the start. How and when did she become friends with Sarah? Was she as much of an obnoxiously spoiled brat-bitch as Sarah or was she more of a calming/restraining influence? Does Scarlet know about her, and, if so, how much does she know about her? Could this friend shed more light on how and why Sarah ended up to be the spoiled Bitch that she was when she and Scarlet first arrived on Dikadia? If all of that ends up being discovered, it could mean some very interesting things... along with the exploration and expansion of Daisy's teleportation power.