Unique characters are more than just a strong physical image. The basic description of the surface does not reveal the uniqueness of character.
To make a character unique create them with:
a special outlook
a highly developed sense
unusual reactions to conflict
Through their inner monologue show the complexity a glimpse at the surface would never reveal:
show their unique outlook
their reactions to their expanding knowledge
they way they come to conclusions about their dilemmas
The unique character has a way of expressing themselves that is fresh and original.
Unique does not have to be unusual or exotic. It should be grounded in their attitudes, beliefs, habits and quirks not tacked like a toupee to the shiny dome of stale and glib.
unafraid, unappreciated, unassuming, unbalanced, uncertain, uncomfortable, unconcerned, unconvinced, undaunted, understanding, under-whelmed, undeserving, undesirable, uneasy, unflinching, unforgiving, unfriendly, unfulfilled, unhappy, unhesitating, unimpressed, uninhibited, unique, united, unloved, unnerved, unpleasant, unruffled, unruly, unsafe, unsatisfied, unstable, unsure, unwavering, unworthy, unyielding, uplifted, upset, uptight, useless, usurped