Nalle Hukkataival has written a nice and descriptive blog of his bouldering journey in Japan. Among other nice experiences he repeated Banshousha, 8C in Ogawayama. It has been considered as the hardest slab in the world and it was mentioned as a contendor to the world hardest boulder in the 8a yearbook 2008, as it has not been repeated since 2000. Nalle suggests 8B as it only took him one day.