In the context of the "Faya" (often associated with art toys and collectibles like the "Faya Magic Soul" or "Faya Snow Kingdom" series), Muscle Growth refers to a popular niche of fan-made or specific artistic animations and fantasy content featuring these characters.

Heyone Global: The official distributor for many Faya Art Toys and blind-box collectibles. If you'd like to narrow this down, let me know:

• The Source: Growth is derived from ancient runes, demonic pacts, divine blessings, or the absorption of elemental fire.
• The Metaphor: Muscle represents magical capacity. As the character’s power grows, their physical form must expand to contain the energy.

It wasn't a slow process. It was a rapid, surging inflation of power. She watched through blurred vision as her forearms began to thicken. The lean definition smoothed out, replaced by thick, heavy cords of muscle that bunched and rolled under her skin. The leather bracers she wore groaned under the sudden pressure, the straps straining against the expanding circumference of her arms.