The homeworld the Coyenas comes from possesses an interesting mix of science and magic intertwined, which allows for certain effects and processes not possible with science alone. One of the things made possible by this is various types of growth effects: increases in size, muscle mass, endowments, etc. Thanks to Boreas’ and Austeria’s work as bioscientists, and Zephyrus’ amulet and Austeria’s wristlet, these effects are very familiar to the Coyena family.

If you’re an artist or writer and have been considering doing or have been requested to draw or write a scenario featuring growth, here are a few guidelines and rules on how things work.

Triggers

Devices. Most obviously, the amulet and wristlet are a source of growth and size-shifting abilities. Taken as complete functional devices, they grant their wearer the power to grow larger in overall size, to grow heavier in muscularity or mass, to increase the size of their endowments, or any combination of these. This power is controlled by mental thought, once the wearer learns how to do it. However, these powers are also keyed to only work for individuals within a single genetic bloodline; currently that includes only Boreas, Zephyrus, Austeria, and Eurus.

Note that the amulet’s and wristlet’s power is driven by the Amasethyst gem embedded within, but the mental control and genetic lock are encoded within the casings surrounding the gem. The gems on their own hold potential energies but need some trigger to have an effect. Likewise, if either device is in a not-completely-functional state—for example, if Boreas or Austeria have them cracked open to work on them—the mental and genetic limitations may not apply as expected.

As mentioned elsewhere, Zephyrus’ amulet can be a bit glitchy, and may cause unexpected effects either randomly or when triggered by some external force. Austeria’s wristlet tends to be more stable; however, she tends to tinker with hers more, which may cause unexpected effects while parts of the wristlet are disassembled.

Other devices may exist with similar growth properties, whether powered by other Amasethyst crystals or by some other means, but they are relatively rare.

Pharmaceuticals or supplements. There are also a wide assortment of substances which may cause various types of growth: potions and elixirs, enhanced health food supplements, timed-release lotions or salves, and so on. These will have varying levels of potency, speed, and duration.

Eurus, not having a device of his own, will gladly make use of any of these substances he finds for himself; often not paying close attention to any dosage recommendations or potential side effect warnings. These substances may also be used as practical jokes—slipped unsuspectingly into someone else’s food or drink—or accidentally, if someone grabs the wrong bottle or can or doesn’t realize that substance’s properties.

Fields. There may be objects or areas that emit an invisible field that may trigger growth. These would be extremely rare in a natural setting, but not impossible; and they may have a more immediate effect on someone who has been regularly exposed to growth powers already (i.e., the Coyena siblings).

Rules

Whatever the trigger whatever type of growth, here are a few rules to keep in mind, either because of the way magic and science work, or by my own personal preferences:

• All growth is temporary. If a device is used, the user will revert to normal, when the device is removed or powered off or runs out of energy. This will also typically happen, especially if the device is mentally controlled, if the user falls asleep or becomes unconscious.
  No growth effect is permanent; the only way to do that is the hard way, which is why most of the Coyenas spend so much time at the gym. ;)
• Typically, clothes do not grow with an individual. Most growth effects work on the user within a biochemical sphere. A device will typically be programmed to grow with the user, but any clothes, possessions, etc. will usually not be effected. If an increase in size is not anticipated or expected, clothes will likely be shredded. ;)
  If an artist is concerned about drawing explicit nudity: The coyenas have invested in extremely resilient spandex undergarments they sometimes wear, which may help keep them modest. :)
• Growth effects are (relatively) safe. While Eurus or the others may seem somewhat reckless in wearing glitchy devices or trying any powder or potion they come across, no lasting harm will ever come to them. Effects are always temporary and side effects will never be painful, debilitating, or lethal. 
• Do no personal harm. The Coyenas may occasionally, due to accidental or unfamiliar growth or size, damage some furniture or knock over a building or two. However, they will never intentionally cause serious damage, and they will never injure or kill another person or animal. It’s not what they do.

Any further questions? Feel free to ask Cooner. :)