Enhancement Slot

The Enhancement Slot is a gameplay component of The Legend of Dark Witch series. It is found in every single mainline game.

The Legend of Dark Witch: Chronicle 2D Act
The Enhancement Slot is a gauge with a black background. Whenever something is, can, or could've been installed, it is colored orange. Whenever a slot cannot be installed anymore, it is grayed out.

The Legend of Dark Witch Episode 2: The Price of Desire
The Enhancement Slot in Episode 2 is color-coded, depending on what type of slot you are installing. Blue is speed, yellow is for additions to Zizou's moveset, green is for weapons, and red is for Power. Whenever something is, can, or could've been installed, it is colored purple. Whenever a slot cannot be installed anymore, it is grayed out.

The Legend of Dark Witch Episode 3: Wisdom and Lunacy
The enhancement slot in Episode 3 is a blue bar. When you install something, it turns orange. Installing that same ability again will make it hot pink, and it can't be installed again.

Overall
The Enhancement Slot is powered up with Tres. Collecting Tres will increase the meter, and if a bar is highlighted, you can install it with A.

The Legend of Dark Witch: Chronicle 2D Act
In Chronicle 2D Act, finding a Syega piece will upgrade a specific slot, allowing you to install that ability again.

The Legend of Dark Witch Episode 2: The Price of Desire
Due to Episode 2 using Pure Syega instead of regular Syega, Syega acts as a currency that allows you to upgrade the abilities you want. You can also swap out slots depending on their color.