I'm looking for a shoujo manga where there's a girl who dies in an accident or something and this guy has a pendant that can be used for time travelling and uses it to save her. They fall in love but the catch about the time travel was that whoever uses it would die or something like that (memory's kinda fuzzy) but as payment for travelling back in time, he dies instead of the girl. I think this is a oneshot. Can someone please help me?

"You are the first dream of my soul, and from that dream I hope will come all other dreams, a lifetime's worth."