A year is a really long time in collectible-
pricing terms.  General series interest 
fluctuates, new cels pop up which impact the 
prices of other cels, collectors come and go.  
Maybe a year ago there were a couple die-hard 
fans who boosted the price up, and they are gone 
now.  It can really be a number of reasons.

I feel your pain though, I am trying to sell my 
cels too and it is hard because I have such a 
focused collection.  I paid a lot for many of my 
cels because I had to battle it out with another 
Yukito fanatic - Unfortunately that means when 
it comes time to sell, theres no one left to 
raise the prices.

If its not selling, all I can say is start it 
off low, let it ride and accept whatever it 
gets - or hold onto it for awhile if its not 
worth letting go at a lower price.  It's not 
worth it to keep relisting over and over around 
the same price if no one is bidding - best to 
wait awhile.  Maybe a new collector will pop 
into the scene and will love to pay your price 
for the cel in a month or two.