Blacksteel is based on my shiny female Wooloo in Pokemon Shield. The moment I saw one being an actual black sheep, I had to do whatever I could to catch it.
Black is of a lonely nature, so she is usually by herself. She hardly ever smiles and often seen as grumpy and maybe a bit anti-social. But that's just her default face.
She's actually very nice.
Wooloo © Nintendo/Game Freak/The Pokemon Company
Art by https://twitter.com/VRHyoumaru