Kensuke Hamada has made what I think is the 4th ascent of Tokio Muroi's Bansousha at Ogawayama, Japan. Weighing in around 8B(ish), this if one of the most difficult slab boulders in the world, if not THE most difficult. I've no idea. (If you ask me, all slabs are heinous, so let's not go there).
Earlier, Kensuke has proven his skills when it comes to steep and dynamic climbing. By this, I'd say he's earned his wings as a slab climber as well.
Originally Bansousha was given 8C/5.dan and it took 6 years until it saw its 2nd ascent by Toru Nakajima, 14 years old at the time. The 3rd ascent, by Nalle Hukkataival, came in April this year.
According to a comment below, Tokio climbed a possibly even harder slab, Kakusei (??), just to the right of Bansousha (the "line" just behind Nalle), in December 2007. This ungraded problem has yet to be repeated.