Shichi Henge

七変化 Literally "Seven Transformations"

Refers to a series of rapid costume changes or transformations. A lot of Sentai heroines (especially pink rangers) have been known to do a lot of costume changes in an effort to bewilder an enemy.

The number seven probably comes from the number of colors there are in a rainbow. In practice, the term just means a series of "quick transformations".

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Dictionary Definition

1: (Usually written using kana alone) lantana (plant, flower);
2: kabuki dance in which the dancer quickly changes his clothes seven times

From Jisho.org