Skirt steaks are a long, thin cut from the plate primal. They offer bold, beefy flavor at a more affordable price than highly prized ribeyes, tenderloins, etc. Inner skirt steaks are the quintessential fajita cut, while outer skirt steaks are more highly prized and usually served sliced as a center-of-plate steak rather than as an ingredient.
Wagyu beef is from a breed of cow specially raised to increase its percentage of fat marbling to consistently high levels. More marbling leads to more flavor, tenderness, and moisture as the fat melts during the cooking process. This wagyu beef is from domestic cattle that are descendants from Japanese herds and raised in the United States. Their intricately marbled beef (commonly known as "Kobe beef", American Kobe beef or Kobe-style beef) is legendary and the result of careful breeding and a highly regimented diet. That marbling creates beef that is the most tender, juicy, and flavorful available.