The history & depth of the Regina/Emma relationship 

You listed Snow Queen, RB, OQ and SQ as the four most important relationships to Regina. I totally agree with you on 3, the one I am doubtful of is Swan Queen. I think Regina has a much stronger relationships with Malificent and Tinkerbell. I understand the importance of getting along with Henry's other mother, I just don't see the depth or history in that relationship that Regina has with the other two women.

I disagree. Regina has no real deep relationship with Tinkerbell. She had one with Maleficent, but Kristin Bauer is a guest star on the show and as much as I would love to see her more, I don’t expect much. 

With Emma, ever since season 1 they were the two focal points of the show’s Storybrooke story, just as much as Snow and Regina were the focal point of the flashbacks. Ever since season 2 their relationship develops something closer and deeper. Especially in Neverland they came a long way. Sharing Henry bonds them, but sharing magic bonds them too. The events of season 4 a kept them mostly apart, but season 4b proved again that their friendship is a very relevant and important part of the show. We see Regina teaching Emma magic and Emma feeling no one can understand this magic inside as good as Regina. We see them joining forces against the dark forces that threatens the town or their loved ones. We see them protecting each other in their own way. We see them slowly opening up to each other, being first allies, then partners, then friends. We see them making huge sacrifices that benefits the other. And this relationship is still in development. It may have not the history of the Regina-Maleficent one (altough let’s face it, the bigger part of this relationship exist only in headcanons - probable headcanons, but still, only headcanons), but it DOES have a history in the canon show, and what is more, it has a future too. 

The greatest sacrifice and gift Emma ever got from anyone…

Regina protecting Emma from the dark path…

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