I'm not sure if I'm missing something really simple, but I was just messing with some of the examples for Custom Character Metadata, but I can't get it to work. I basically copied the example:-

using Naninovel;
using UnityEngine;

public class MyCharacterData : CustomMetadata<SpriteActor>
{
    public int MyCustomInt;
    [Range(0f, 100f), Tooltip("Tooltip for my custom range.")]
    public float MyCustomRange = 50f;
    [ColorUsage(false, true)]
    public Color MyCustomColor = Color.white;
}

CS0246: The type or namespace name 'CustomMetadata<>' could not be found (are you missing a using directive or an assembly reference?

I can't find any reference to CustomMetadata anywhere, I thought maybe it was a error in the example, but later on there is something else with the same inheritance?

Make sure you're using the latest version of Naninovel package.