It's from Jigoku Sensei Nube (Hell Teacher 
Nube).  The man is Tamamo Kyousuke, and he is 
Youko (fox spirit) that has taken over a human's 
body.  The boy he is talking to is Tateno 
Hiroshi.  Not 100% sure what episode it is, but 
I'm guessing eps 7 (been awhile since I've seen 
the series).

Neat cel.  Where did you find it?  I'm just happy 
to have found a nice Nube a while back.  Tamamo 
is next on my list. ^^

Laters,