The Transformation Brooch was Usagi's first item that she used to transform into Sailor Moon in the anime and manga. Luna gave Usagi the Brooch at the beginning of both series and tricked her into transforming in order to prove to the girl that she had a destiny as a Sailor Senshi. Once she obtained it, Usagi also began wearing the Brooch in the center of the bow on the front of her school uniform when she was in civilian form.
The Brooch was broken in episode 51 of the anime and Act 13 of the manga, but became the Crystal Star after the Silver Crystal merged with it. All of Usagi's transformation brooches were upgrades of previous brooches.