Donabe Hamburg Hokutosei (土鍋ハンバーグ 北斗星) has a couple of location in downtown Sapporo, and judging by how crowded it seems to get every night I'd say they're probably doing pretty well. They serve hamburg steak served in an earthenware pot (the 'Donabe' part of the name) in a rich soupy sauce and when I went a while back it was really very good.
I can't guarantee those dudes with the amazing hair will be their on your visit, but this branch is pretty near Club Counteraction so they might be!
The shop is pretty small with only counter seating, so it's fun to watch the whole cooking process including the massive gouts of flame they unleash while they're cooking the hamburg.
That's only one chef, but the mirror really helped to dispel any feelings of claustrophobia in there! I'd describe the cuisine at Hokutosei as rich. Very rich. I went with the stuff that was recommended on the wall, a tomato and cheese thing with extra bacon topping, and Yuki had something else. I forget what that was but... something to do with vegetables.
The sauce is thick, the hamburg steak is juicy and delicious and that crazy, crazy thick bacon (I do not think that would be classed as bacon in England, that's like a level up - gammon or something) was amazing. Allow me to talk a moment more about the bacon - it was so thick, and so salty - man, it was like ur-bacon or something. The archetype of bacon. And eating it was such a challenge that it came with a pair of scissors to cut it into edible chunks.
Look at how thick that is! I've had thinner pork chops! If you're into strong flavours and big, hearty, meaty dishes I'd recommend the place. I'll stick the one I went to on the map, but the other one is in Tanuki Koji, on the other side of eki-mae dori. It's easy enough to find and there's always the internet, which I'm assuming is how you found me.