Very often, a story will have two badasses in a relationship. One will proclaim that they won't let anything happen to the other and/or vice versa, and will even take any opportunity for Flirting Under Fire. But perhaps having the same fighting style, or even both having Super Powers, could be boring to viewers, so how can the author make them more interesting? Give one of them Super Powers (likely the girl) and make the other a Badass Normal (likely the guy).
She could have any superpower she can. She could have Super-Strength, Super-Speed, Flight, Psychic Powers, Elemental Powers, White Magic, Black Magic, etc. Her powers make her stand out in the relationship. Of course the writers may feel the need to have the two be on the same level, so they could make him have his own skills. He could be a Gadgeteer Genius, a Bare-Fisted Monk, a Multi-Melee Master, an Ace Pilot, a Gunslinger, etc.
The ways she could get the power can vary. If they are in a Fantasy work, she could be a Magical Girl, a Black Magician Girl, or any type of Squishy Wizard, while he could be a simple Barbarian Hero with no powers, using only his sword. In a Science Fiction work, she could be Cyborg, a Ridiculously Human Robot, or a Super-Soldier genetically modified, while he could just be a Science Hero. In a Superhero work, she could have Radiation-Induced Superpowers, a Human Alien who's powers come naturally to her, or has taken a Super Serum, while he could be just be using Powered Armor.
Compare and contrast to Strong Girl, Smart Guy, Muggle–Mage Romance, and Sword and Sorcerer. They may be a case of Interspecies Romance or Savvy Guy, Energetic Girl
