Tenderloin tips are exactly what their name says they are: tender. As the tip of a filet, they're considered scraps and are sold for cheaper. Amped up with a little seasoning, like the soy sauce, sake, and rice wine vinegar in this recipe, and they instantly outrank their filet counterparts.
To prepare the marinade, place all of the ingredients except the beef, rice, and cold water in a saucepan and heat through, whisking until the sugar dissolves. Let cool. Transfer to a mixing bowl, add the beef, and marinate in the refrigerator 2 to 3 hours, turning occasionally.
Place the rice in a strainer and pour running cold water over it until the water no longer looks milky. Soak in a bowl of water for 1 hour. Drain and transfer to a saucepan, together with the 2 cups of cold water. Bring to boil, turn the heat to low, and cover. Simmer about 15 minutes, or until the water has been absorbed and the rice is sticky and soft. Keep warm.
Drain the beef and thread onto metal or bamboo skewers that have been soaked in water for 30 minutes. (Using 2 parallel skewers instead of one prevents the meat from spinning around and not cooking evenly.) Pour the marinade into a saucepan and bring to a boil. Cook over medium-high heat 5 minutes, until reduced and syrupy. Grill the kabobs over direct medium-high heat for 8 to 10 minutes, turning occasionally, brushing the meat with the marinade glaze with each turn.
Remove the beef from the skewers and transfer to serving plates with the rice.