Usa risks her own life by using the Crystal from the future. In  fact, both girls do use their full power. What really happens in the scene in  which Sailor Moon and Rini are floating against the pink hazy background is  that the voice of the original Queen Serenity comes to them and says that  since the greatest wish each of them had in their hearts was to save the  other, they will both be restored to life, through the powers of the present  and future Silver Crystals. In the original, Usagi and Chibi