Ring
Disclaimer: I don't own Yu Yu Hakusho.
He often wondered what their wedding rings would look like. In the dead of the night, when he was too exhausted to study anymore but couldn't fall asleep either, he could picture her in flowing snow white and the palest of spring greens like the angel that she was, blessing him with her happiest smile and loving eyes as he knelt down and proposed. And then he'd look down at his hands, which clasped a delicate velvet box, and find that there was absolutely nothing inside.
In the light of morning, he felt stupid for dreaming of such a thing (after all, he didn't even know if she reciprocated his emotions), feeling much like a lovesick teenage girl as he walked down the street. And then he'd spot the window display of glittering gold and platinum and silver and gems of all the colors in the rainbow, and he'd stop and stare at all the jewelry for the longest time. He'd be disappointed, then, to realize that the most beautiful diamond, the queen of stones, was unfit to grace her finger and that it would be outshone by the ice crystals, hiruiseki, and snowflakes she could produce anyways.
He'd realize, eventually, that there was no ring better than a loop of the Red Pinky String Of Love, and that one day, he wouldn't have to dream anymore.