The Seven Great Youma were first introduced in episode 025, in the first season. Queen Beryl instructed Zoisite to locate the seven Nijizuishou in order to form the Ginzuishou and fully revive Queen Metallia with its power. During the next seven episodes, a massive search ensued. Zoisite was able to locate the Nijizuishou by using the Kurozuisou. He would locate one of the Nijizuishou and extract it from its carrier, causing the person to revert to his Great Youma form. The senshi attempted to stop Zoisite, but were usually attacked by the youma. Rather than killing the youma, Sailor Moon used her Moon Healing Escalation attack to seal the youma within its carrier once again. In episode 034, the Dark Kingdom managed to collect all seven of the Nijizuishou. However, when Tuxedo Kamen was injured, Sailor Moon began to cry, and the crystals floated to her instead. The seven crystals then joined with her tear in order to form the Maboroshi no Ginzuishou.
(via the oracle)