Bester stones (Otokoyama is the exact same thing) are the most recommended stone by Tsuchida Noboru-san who runs a super famous tool shop in Sangenjaya, Tokyo. (His father Tsuchida Ichirou is a renowned collector of Chiyozuru Korehide tools. They both have published many books on Korehide. )

These stones are as hard as Shapton stones so there is less time spent on fixing the surface, which is very important with medium grit stones because this grit is the stone where you'll be spending the most time. And the cutting strength is as strong as Shapton. What is best about this stone is that it gets clogged less. Besters are great with anykind of steel. These are not so popular compared to Kings and Shaptons, so you might not find them elsewhere.

#500(Beston) 4550, #700 3600, #1000 4000, #1200 4000, #2000 5700