Never heard of "Nanami and the Inferno of First Love" but the info I found on it makes me want to see it. It was even nominated for the Golden Berlin Bear in 1968. And I've never heard of the director either. But there's so much to explore and discover in Japanese film history for a westerner 
Susumu Hani definitely reads like somebody to look out for.
Thanks for bringing it up.
I have two or three films by Teshigahara on DVD. The company Masters of Cinema in the UK have released two (?) of his films in beautiful editions.