BlackLeg is one of the two skins released under the Anime Nation III part of the Anime offer. It could be purchased as part of an item deal for a limited time in early September 2020.
BlackLeg could be purchased for $7.99 in a deal that included 8000 coins. It could also be purchased for $19.99 in the "Best Deal!" which included the Dattebayo skin, 20000 coins and 1800 DNA. It was not available for individual purchase and may not be available for purchase in the future.
Details of this skin may vary depending on location, platform or time.