One thing that could help: there was a press conference thingy for The Boy Who Saw the Wind. 有川博 mentions he doesn't do much animated work, so it might be the same actor. There are a couple of pictures, but I'm terrible at recognizing people's faces.

https://www.cinematoday.jp/page/A0000031
http://www.werde.com/movie/interview/kaze_shonen.html

Oh yes, it is the same person. On the werde.com page I think he's standing farthest to the left in the back. I looked on https://ja.wikipedia.org/wiki/%E6%9C%89%E5%B7%9D%E5%8D%9A and it shows the credit also plus other voice work.