Ok, so for fun, I started drawing thunder in both her human and pikachu form. Keep in mind, after I show you the rough sketches I made, I will most likely describe what thunder looks like, and it may look different from the actual sketch.

So, in her human form, thunder has blond hair that almost looks like auburn, blue eyes, a dress with red and blue diagonal lines and a yellow base and a skirt pattern on the end of it, and yellow-orange knee-high socks that are the only thing her human form has to cover her feet.
In her pikachu form, she has soft fur, patches of fur on her chest and forehead, blue eyes, and a pink ribbon on her right ear. Other than those things I pointed out, she pretty much looks like a normal pikachu. Anyway, I hope you guys enjoy. Bye!