Sailor Cosmos
SailorChibiChibimoon receive it when she saw Sailormoon fighting with all her hope against Chaos. Sailormoon receive it when she was fighting against Chaos. At the beginning they were all only Sailormoons. They were maybe the strongest senshi but the Cosmos power made them even more powerful.
The gift to become SailorCosmos is given generation after generation so SailorChibi»Chibimoon, whoi actually came from the future, might really be SailorChibimoon (I doubt that) or her daughter!
This is what I think SailorCosmos really is.