These Treasures decrease the initial 700% stat magnification applied to all unstarred Aliens' base health and base attack power.
For example, a hypothetical unstarred Alien has base health and attack power of 1,000, but the default stat magnification applied to unstarred Aliens' base stats is 700%, making the enemy's health and damage per hit 7,000.
Each fully activated Aqua Crystal and Plasma CrystalTreasure set then reduces this 700% default magnification by 100% (subtractive) such that this example unstarred Alien's base attack power is always 1,000 but the default magnification effect applied to produce the enemy health and damage output is reduced as shown below.