Roy Mustang & Riza Hawkeye are characters in the manga (and also anime) Fullmetal Alchemist, created by Arakawa Hiromu-sensei. While they're not main characters per se, they have their own importance in the story, especially once the plot progresses.

Roy is a colonel within the National Amestris Army, and is also known as the Flame Alchemist. He knows the pains of war first-hand and aspires to change his country for the best, by overthrowing its tyrannical dictator. Hawkeye knows him since before he was even an alchemist, and entrusted her hope for the future in him. After all those years, through some painful disappointments, she's still by his side. As his right hand woman, pillar of strength and the person he trusts more than anyone.

Roy & Hawkeye's story is one that's difficult to explain with words. Two young idealist people meeting, not very scarred by life yet, sharing their dreams and hopes for the future with the other. Colliding by chance (or not really) years later in the middle of a massacre, almost two different persons already, lost, confused but still determined to go on -- together. Trying to reach happiness, not really for themselves but for everyone, while sacrificing a normal life for it.

It's a story of growth, of wanting to change the world and be willing to, not only try, but dedicate your whole life to it. It's a story of love (of whatever kind you choose to see it) overcoming all obstacles, of devotion and faith in placing all your hopes and trust in one single person.