In addition to the recently mentioned new Sebata Yūzō book, 源流テンカラ釣りの知恵 , Headwaters Tenkara Fishing Wisdom.
You might also find the following two magazines fun.
One advantage is they are more picture rich with color photos. With short captions that are easier to figure out thereby ferreting out more information from a language most of us cannot read.
{ that being said, if you have an interest in making a Sebata Yūzō type taper line - there are pretty good diagrams explaining the process on pages 189 ~ 191 of the Headwaters Tenkara Fishing Wisdom book.}
Tsuribito’s 渓流 ２０１８夏号 （別冊・つり人Vol.472）Keiryū 2018 summer issue.
It also has several pages featuring Sebata Yūzō-san, including how to tie his style of self-fusing tape kebari (which is also covered in the book)
The picture on the cover is also in the Sebata book. He is Mr わがつまとくお / 我妻徳雄/ Tokuo Wagatsuma-san. He is profiled in the Sebata book beginning on page 135.
http://fishing.shimano.co.jp/instructor/keiryu/inst_wagatsuma_tokuo.html
Tsuribito Keiryū 2018 Summer English translated
Maybe it will be helpful if your are aware Google is translating Tokuo Wagatsuma, as My wife Tokuo, and Ishigaki Hisao as Ishigaki Naoo.
And that Sebata Yūzō is referred to by all these odd translations of his name or nickname : Mr. Yuzo Setoh. Yuzo Sehata “Okina no Okina”. Sehata Flow.
山釣りJOY Vol 2 Mountain Fishing Joy
『夏×源流＝イワナ天国!』“Summer x Genryū = Iwana Heaven!”
今年はどこの渓に行く？ This year, go anywhere in the valley?
今年の山釣り計画は、この1冊で決まり！Mountain fishing plan for this year is determined / decide by this one book!
Very much similar flavor publication as the Tsuribito Keiryū magazines.
Yamakei 山釣りJOY Vol 2 English translation
Another summary of the issue from the River-Walk website.
Maybe the odd translation differences will provide more insight to the issue.
『山釣りJOY 2018』の見本誌をいただきました！』
We received a sample magazine of “Mountain fFishing JOY 2018”!
(however, the Google translation blocks the image of the front cover of the magazine)
river-walk 『山釣りJOY 2018』English translated
Also included are some writings about 山本素石さん, Yamamoto Soseki-san, for those with an interest in him and his books. The subject seems to be 源流レインボー, genryū rainbows. But I think it is rainbows in the sky above the mountains. Rather than rainbow fish. 
