Prior to the series, Sunset began dating Flash when she first came to the human world. But as she became more of a bully, Flash broke up with her since he did not like the person she had become. When Twilight Sparkle followed Sun set to the human world and she and Flash took an interest in each other, Twilight was warned not to pursue Flash lest she make Sunset jealous and angry.
After Sunset was redeemed and turned over a new leaf, she confessed to having only dated Flash in order to become more popular. This however may not be entirely true as she has shown to show regret towards the breakup.
Sunset later suggested to a depressed Flash to give up on Twilight since she lived in another world and would likely rarely if ever return. Following this, Flash thanked her for the tough love and expressed his desire to start over with her as friends. It's implied that he had once again taken an interest in Sunset and rekindling their past relationship. Sunset seemed to become flattered and shy by his comment and showed implied interest at possibly liking him as well before she was distracted, and hurried away, leaving a dejected Flash behind calling to get back to her later.
In the music video Good Vibes, Sunset gives a depressed Flash a free lunch from her place of work, and the two eat together happily. In the specials and shorts that have followed, there have been several hints and indications that their feelings are rekindling.
During the Rainbooms' music concert in Spring Breakdown, Sunset spots Flash in the crowd and flirtatiously winks at him, causing Flash to blush.
In the musical short, Cheer You On, the Equestria Girls attend Flash's band's concert. Before the music starts, Sunset attempts to look nonchalant by playing on her phone, but Sci-Twi knowingly punches her shoulder while Rainbow Dash and Applejack give her equalling knowing looks, causing Sunset to blush and divert her eyes. In the battle that follows where they face down a robot that's run wild, Flash risks his life to recover Sunset's magic necklace that he returns to her. After the battle, the two are seen sitting together with Sunset's arm draped over his shoulder, smiling at him.
In the special, Holidays Unwrapped, Sunset recruits Flash to assist her in a snowball fight. Flash immediately comes to her aid and appears to get shy and flustered by her when he responds to her question of if he's ready, "I was born are you... ready".
- Sunset Shimmer/Flash Sentry tag on AO3
- Sunset Shimmer/Flash Sentry on FanFiction.Net
- Sunset Shimmer/Flash Sentry on FimFiction.Net
- Upon the release of "My Little Pony: Equestria Girls 🌟 Season 2 Trailer" in early January 2019, storyboard artist and director of the series Katrina Hadley stated "😏" regarding the possibility that Sunset and Flash and would get back together.