This was written as a challenge for an alternate pairing, or non-canon pairing. It's Miroku/Ayame.
Love Stays Underneath the Shady Tree
He knew when he saw her he had to have her. Sure, he couldn't say anything since he was there with Sango and that would just look bad. He even told Sango she'd be the one; the only one. But that wasn't true.
That one night the red haired beauty from northern mountains came down and everyone was busy with Kouga when he pulled her aside. He told her. For some reason she knew. Call it a woman's intuition; call it a demon's intuition, but she knew. They pledged their love underneath a shady tree and came back to the group without anyone knowing they had left.
They both knew that was their first, last, and only time they'd be together. Years later Ayame and Kouga had a litter and he married Sango and was on their way to having a litter of their own. He loved her with all his heart, but part of him wondered what would have happened if they just left that night after their meeting underneath the shady tree.