Cut the beef into bite-sized pieces. Remove strings from the celery stalk and cut diagonally into thin slices (usu-giri). Finely chop the celery leaves.
Melt the beef fat in a non-stick frying pan and add the celery stalk and leaves. Add the beef and cook until browned. Mix in the (A) seasonings and continue cooking.
When almost all liquid has cooked off, remove from the heat and add the juice of the squeezed grapefruit. Return the pan to the heat and quickly stir-fry. Place the beef on a plate and garnish with the grapefruit pulp.