Set the sous vide cooker to 54.4°C / 130°F to preheat the water.
Place the Wagyu in a vacuum sealed bag and sous vide for 90 minutes; three hours if frozen.
When the Wagyu is done, chill the steak in the vacuum sealed bag. If the steak is 3/4" thick or less, 15 min in cold tap water. For steaks 1" thick or more, 5 minutes in cold tap water.
Preheat the skillet over medium-high to high heat while steak is chilling.
Remove steak from bag and season it with salt before searing.
When the pan is ready, sear the Wagyu steak no more than 60 seconds per side to get that golden-brown tasty crust. For 3/4" cuts we'd sear closer to 45 seconds per side. Butter optional for a deeper brown crust.
That's it; all that's left to do is to enjoy your "melt in your mouth" Wagyu steak!