(Based on information from Regina Rising!!)
Regina wasn't the type to admit to her insecurities. She'd rather just keep quiet about them and ignore them when she could. But this one was particularly annoying to her, and it was always there. When she looked in the mirror, she could feel it above her lip. And she hated it.
It wasn't so much that she hated the scar itself; she'd asked for it back, after all. It was what it represented. Her first true act of rebellion against her mother. She'd first got the scar after being thrown off Hwin, when she was just 12 years old. Then, aged 16, she'd wished for the Blue Fairy to return it as a symbol of her bravery. Even Cora's magic couldn't override that. But that wasn't what it symbolised anymore. Not in Regina's eyes.
The Blue Fairy had sensed something within her that day. Regina had implored for her to tell her just what that was; the poor fairy had been trembling at her mere touch. She wasn't entirely sure what the problem was. Regina was pure of heart, at the time. But she told her to return to that moment, when her heart was pure and her wish was granted, when she was torn between light and dark. Regina didn't understand it then. She did now.
The scar reminded her now of that moment. The Blue Fairy had been trying to save her from the dark potential she'd sensed within her. And Regina had ignored it. Now, all she felt for it was disdain. But you didn't see it that way. You still loved Regina, no matter what the scar meant. In your eyes, the very fact that she felt guilty when she looked at it showed that it was serving its purpose. Regina had changed, and she'd come a long way from her dark path.
Still, when Regina expressed her insecurities, you sat, straddled over her lap, tracing star shapes around the scar tenderly. Regina's heart bled whenever you did it.
"You're a bleeding heart, you know that?"
She quipped, resting her head against yours, adoration in her gaze.