A/N: English is not my mother tongue, so I apologize for any grammar and spelling mistakes.
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Roy and Riza. That's how it has always been. The two of them had a bond, forged with trust and companionship. It goes back years, when Riza entrusted Roy with the secrets of flame alchemy. It was a sign that she believed in him. She believed that alchemy would save the people. That it was there to change the world for the better and that Roy would use it for good.
But that belief was shattered when years later, she had to fight in the Ishval cilvil war, killing countless of people. She witnessed the despair and sorrow of mankind; it was hell.
Overwhelmed with grief and guilt, she asked Roy to bury the secrets of flame alchemy and he granted her that wish.
She herself decided that she would follow Roy to hell. She would protect him, have his back. She devoted her whole life to him and he in return had made a promise. A promise to reach his goal and to make amends for both of them. Even though they could not undo what they had already done, they tried to make up for their mistakes. It was a start into the right path they had both taken.
Even thought Riza's job was to protect Roy from any harm, she did not do it because she had to. She protected Roy because she wanted to. She cared about him. She loved him, that much that she agreed to shoot Roy in the back if he ever lost his way.
Love was not something they needed to discuss. They both knew it was there. From the beginning when they had first met, up until now. That's what made them special. They didn't need to say anything and they didn't need someone else to saying it. They already knew that the thing they had was an unbreakable bond.
That's what they swore to each other.
"Until death do us part"