Umi is sarcastic, selfish, bitter and somewhat mean.  He is at first very unwilling in his position as a guardian fish, caring nothing for anyone but himself.  He and Omnes both claim that the reason he was reincarnated as a fish was because of horrible crimes committed while a human, but it's difficult for anyone to see Umi as someone even remotely intimidating. 
Jigoku is more stoic, but also less selfish--though still bitter and cynical over his life.
 

Crude and sarcastic, Fuu is very immature--probably because he's only fourteen.  His animal form resembles that of a cross between a ferret and a very fluffy cat, with a small, furry body and an incredibly long tail (which he keeps in his humanoid form).  Fuu loves attention and will do anything to get it, including threatening to bite the necks of the person whose shoulder he is currently occupying (although he would never really do this, it's a fairly effective threat, as he has a mouth full of dagger-sharp teeth).

Reiko is as brilliant as Roan but much more sane.  She works as Roan's lab assistant, and lives in Roan's house with her.  She is very demure and tolerant of everyone, keeping up at least a facade of civility even with those she does not like.  Roan treats her with more respect than anyone else, and does not, surprisingly, take advantage of Reiko's complete loyalty to her.

Charon suffers from something of a personality disorder.  He feels that there is another person inside him, one who surfaces when he feels the presence of Sailorlumina.  This personality is cold, ruthless, and seemingly homicidal.  His regular personality, while not wanting to go kill anyone, isn't all that cheery either.  He hates himself, especially his body, and thus wears as much clothing as possible, even in very hot weather.  He can't remember why he has the scars, or even much about his childhood at all, and he has no idea as to why his other personality wants to stalk Jada...

Omnes is Fate.  He's also very vain, self-righteous, and somewhat mad.  He is the physical incarnation and true form of THEM, the orchestrator behind the lives of most of the other characters.  His favorite pastime is devising horrible situations, setting them up and seeing how they play out.  He's a bit sick.

Kiera's bitchy butler.  Xavier never misses a chance to insult Kiera's guests, be it directly or through thinly veiled sarcasm.  He is an excellent worker and performs every task to perfection, however, so he is rarely reprimanded.  His entire family works for Kiera's (mother is a maid, father is a cook, etc).