FlashShimmer

FlashShimmer is the het ship between Flash Sentry and Sunset Shimmer from the My Little Pony: Friendship is Magic and My Little Pony: Equestria Girls fandoms.

Canon
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 less 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.

Fanon
This the most popular shipping for Sunset Shimmer, it's biggest rival is SciTwiShimmer. For Flash, it's the second most popular shipping, the most popular being FlashLight.