"Tataki" in Japanese cooking parlance could mean two totally different cooking methods; one is to sear or grill only the surface of sashimi-grade fish or beef and serve it like "sashimi", bonito or "katsuo" 鰹 tataki is the most famous of this type of cooking, another is to chop sashimi-grade fish, such as horse mackerel or "aji" 鯵, into small pieces often with the addition of seasoning (this is similar to steak tartar). For beef tataki, I just sear the steak and keep the center rare. I slice it thin and marinated it in Ponzu sauce for 5-10 minutes. Garnish with diakon spout or scallion and serve at room temperature.
This version I made today goes well with either red wine (a hardy Australian Shiraz such as d'Arenberg "Dead Arm" 06 is good for this dish) or cold sake. If you use Ponzu sauce, it tends to be too acidic for wine and sake may be better.