at least 8B+
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.
Tokio muroi got FA of ???Kakusei) november 2007.It is on the right of Bansousha and just center line of the boulder named "fukanou slab" (means "impossible slab"). Kakusei may be harder than Bansousha.(Tokio has said nothing about the grade.) Toru has tried it but not completed yet.
Rumors have it you have been trying the slab to the right of Bansosha, ~8B+, at Ogawayama, which is said to be much harder. Can you tell me anything about it? Maybe you have done it already? There are two problems to the right of Bansosha, Kakusei and Huminsho. These problems are harder than Bansosha. I did Huminsho when I was 15 years old. I think Bansosha is V13 [8B) and Huminsho is V14 [8B+], and Kakusei is harder. No one has been able to make a third ascent of Huminsho or second ascent of Kakusei. Tokio Muroi made the first ascents of both of them.