I tried the example in Readme:

階阿定畳乗壱[壱至阿]
主推穢空
主定行
　曰、示、階六

and I get

var-1769040242 a = foldr (*) 1 [1 .. a ]
main :: IO () 
main = do 
 putStrLn $ show $ var-1769040242 6 

.
Obviously the code at https://github.com/kazakami/Hasukeru/blob/master/kanji.cs line131:
return "var" + c.GetHashCode() + " ";
converted 階 to -1769040242.

Have you encountered such case that GetHashCode() returns negative integer?

My environment:
Windows 10 (Chinese. Does it matter?),
.NET Framework 4.5

p.s.
私は日本語とHaskellを初めに勉強しました。面白いrepo！:)