Pickle the carrot:
In a small bowl, combine rice vinegar, sugar, and salt. Stir until dissolved. Add the carrot ribbons and let sit for at least 20 minutes. (Can be made ahead and kept chilled for extra flavour.)

Marinate the steak (optional):
If time allows, marinate the Wagyu flank in Shiso Teriyaki for 30 minutes at room temp or up to 2 hours in the fridge. Otherwise, brush with the sauce just before cooking.

Grill the steak:
Heat a grill pan over medium-high heat. Lightly oil the steak and season with a pinch of salt. Sear for 3–4 minutes per side, depending on thickness, until medium-rare to medium. Brush with extra Shiso Teriyaki during the final minute for a glossy finish..

Assemble and serve:
Plate the steak, drape the pickled carrot ribbons over or alongside, and garnish with spring onion, micro herbs, and sesame seeds, if using.