Most rare?  Probably the eyes-open Rezo -- if the
other "sequence" out there is the same as mine
(one face cel with multiple eye and mouth layers),
there's only two cels of him like that in
existence.  Other candidates would be the Slayers
harmony cel, or my Harry MacDougalls (why the heck
is that boy so hard to FIND, when Genes and Jims
are common as rats?)...

...but instead, I think I'll post this one.  ^_^ 
Firstly, Nadesico cels are tough to find, since
they were never officially released.  Secondly,
item cels are just tough to find, period.  And
thirdly, everybody has SEEN my other rare-ish cels
about a zillion times already and I don't want to
bore you guys to tears.  *grin*

So here's Gai's stash of Gekigangar merchandise,
complete with (heeheee!) a copy of Newtype.