It was in Detroit where I discovered udon noodle soup. After moving here, I had to go without it for a long while until Shi Ki opened and I discovered they served udon noodle soup. They make a pretty good one too (I usually order the nabeyaki udon). Nice rich dashi broth, enough seafood, veggies and noodles to make it hearty but not so much that it becomes more stew-like. I consider it pretty yummy.
Last year Sakura opened on Ashley River Road, and I discovered they also had udon noodle soup, so I stopped by to try it out. Nice restaurant, the udon soup, not so much. Theirs was made from a chicken based broth, so essentially you're just eating chicken noodle soup.
Yesterday after putting out a query on twitter to see if any other Charleston restaurants had udon noodle soup on the menu, I learned the relatively new Bushido (famous for their Spicy Tuna Handroll Challenge) has it on their menu. They make an decent enough soup (went with the tempura udon soup) but I didn't think the broth was quite as flavourful as Shi Ki's, the noodles were a little bland and heavy on veggies. It was much better than Sakura's offering though.
I've been told Mama Kim's on Calhoun also has udon noodle soup, so I think I'll have to make it a lunch destination one of these days to check it out.
Shi Ki - Win
Bushido - Good if you're in the area
Sakura - Give it a pass.