Koikishi Purely Kiss The Animation.

In the past as children, Kaname and Elcia were caught in a building in which a fire had broken out. Elcia got stuck under some rubble, and Kaname didn't plan on giving up on her, even though it seemed hopeless. Just as Kaname was about to run out of strength, a modern-day knight saved them. After the incident, they both decided and promised each other to become knights and to protect and uphold justice and righteousness more than any other. Years later, they fulfill their promise to each other and work side-by-side to protect and uphold justice, while love starts growing in their hearts.