This isn't the Japanese stuff but my first attempt into the Wagyu arena. What is the best way to cook this? Seeing cast iron skillet most commonly? Can I do that on the grill to have best of both worlds?

Butter.

Marinate in something. Just a personal preference.

The Ultimate Pan-Searing Method
1. Prep the Meat
Take the steak out of the fridge. Because Wagyu fat melts easily, many chefs prefer cooking it from cold, while others prefer letting it rest at room temperature for 30 minutes. Choose your preferred method, pat the beef dry with a paper towel, and season it generously with fine salt (coarse salt can prevent an even sear). [1, 2, 3, 4]
2. Grease the Pan
Wagyu needs no added butter or cooking oil. Instead, trim a small piece of the beef fat (or use a bit of wagyu tallow) and place it in a preheated cast-iron skillet over high heat. Let the fat render and coat the bottom of the pan, then remove the leftover fat chunk.
3. Sear Hot & Fast
Place the seasoned steak into the rendered fat. Leave it completely untouched for 60 to 90 seconds to build a rich, golden-brown crust.
4. Flip and Finish
Flip the steak and sear the other side for another 60 to 90 seconds. For an extra-even cook on slightly thicker cuts, you can flip the meat every 30 to 60 seconds. Pull the steak off the heat when it reaches 120-125 F for rare or 130-135 F for medium-rare.
5. Rest and Slice
Because of the intense richness, Wagyu will taste best when sliced into small, thin strips. Let the meat rest for 5 to 10 minutes before slicing to allow the juices to redistribute.