Wife and I just got back from Nakasei Uchimise and it blew our minds! It's a butcher shop in the front and restaurant in the back with some of the best aged beef in Tokyo. More than just the aged beef, the service and experience was great. Our waiter took us up to the butcher shop and explained each cut of beef, from the lean cuts to the fatty marbled cuts, and suggested a few cuts to balance the flavors. He knew a lot about beef! We ultimately went with 2 lean cuts from the front and hind legs and a fatty marbled cut from the shoulder. All were delicious, but my wife and I surprisingly liked the lean cut from the hind leg the best. It had a rich mineral/iron taste that we loved. The fatty marbled cut from the shoulder was ridiculous though and just melted in your mouth. Equally amazing was the aged beef "bacon" dish that we ordered as a starter, which is basically the beef carpaccio we've ever had. Vegetable dishes that we ordered to accompany the beef were solid as well.
Overall this place is very deserving of it's recent Michelin star in my opinion. It seems to be under the radar still, as we were the only non Japanese and our waiter asked us how we found out about the place. If you're looking for a break from sushi in Tokyo, this place is definitely worth visiting.