He projects the image of a temperamental rich boy, powerful and on top of the world, at least on top of the infernal food chain. The closer you get to him, the more you can sort what of that is true and what isn't.
Temperamental--yes. Part of that's inherent and inherited. There's a reason he's lost an uncle and grandfather to homicide, as that side of the family tend to be confrontational in a culture that 'hammers down' such things. His basic temperament is genetic, and he comes from a long line of fierce men. 'Watari' means 'ferryman', which suggests to me that rather than samurai or other such glory, his ancestors were dockworkers, merchant sailors, and shipyard thugs.
Consider also that he has a rather large chip on his shoulder, the issue that drives him to (the necessary for plot) wanting contact with angels. He's Symphonic and it nearly drove him to the nuthouse, but more significantly it cost him his mother. And dammit he will know why, no matter what it takes, and when he finally meets whoever's responsible he's going to pop him in the nose, if it's God himself even.
His temper is also rewarded by sorcery and, for him, its precursor telekinesis. Yes, a potential-six-force little boy with a stepmother he didn't like, who could break glass just by getting angry with it. He can't do that (much) anymore, but at the time it made the connection in his brain--get angry, be feared. Now he's discovered that passion is fuel for magick, giving him plenty of incentive to keep his temper hot.
Rich? That's a bit more complicated. Most of the money is not his personally, and while he makes a comfortable salary he couldn't afford the antique books, the room service, flying first class three times a week, the bungalow on Oahu, or the generous child support he pays if he had just that salary. All the surf-bum nonsense he pulled ten years ago he couldn't do now because he'd lose all the things he's come to depend on. A camel through the eye of a needle.
The infernal food chain? He knows from hard experience and reconstructive surgery that man vs. demon ends badly for the man. He swindles, he sneaks, he plays them off each other, he throws celestial smoke bombs and runs away. The reputation is the important thing on that, as it keeps enough demons insecure enough to not--usually--pull the net around him. One demon, and a bit of preparation? He can dig a victory out of that. Four demons and an ambush? An angel was almost not enough to save him.
He is a formidable sorceror, an amazing innovator who can make magick do things it's never done before. Because he was born hearing it, he has an instinctive command of the Symphony. But superhuman? He knows better.
The closer you get the more you realize you're just dealing with a human being. He doesn't let most get close, because that reputation is his shield and he doesn't trust the world not to turn on him, as it turned on his grandfather. But those close discover that selfishness has been sublimated to the concept of family, that he feels he is defending others with his illusion of wizardry, a lightning rod to draw fire away from those he loves...those who make his life worth living...selfish in that sense.
He is naive to think his father is unaware of Grace, but Ryukawa indulges him for now, remembering how Ryuki was conceived.
As a young child an angel sang to him at night, possibly a servitor of Christopher. A child hearing such songs isn't completely out of possibility, is it? He had to stop when a young Ryuki tried to crawl out the window to catch the singing being, from a 6th story window.
Ryuki's a terrible libertine, a combination of genetics, sorcery, and Eli's "blessing". I'm amazed the PC's haven't caught him in bed yet.

Hawai'i

Lei'alani
I picture Ryuki and Corat indulging drunken karaoke, wailing 'Leila' and enjoying the inside joke.  Because outside of Corat, Pavel, and Kahuna, no one knows who she is.
About nine years ago Ryuki was bent on being a professional beach bum, traveling the world surfing and carousing.  His father barely tolerated this, hoping it was a passing phase and trying to keep it from creating any long-term problems.
A brief fling on Oahu made Ryuki a father, and Lei'alani the child's mother.  Unlike the other women in his life at the time, Lei'alani would not be cowed or brushed off, but made it very clear that Ryuki was going to be a father as nearly as he was capable.  She reminded him of the value of ohana, but she had the wisdom and finesse to place his baby girl in his hands and to accept his decision to hide her from his own father.

Grace "little" Kahuna

One look, one touch, and Grace charmed her father into a lifelong commitment. But isn't that what daughters do?
Her parents will do everything in their power to give her an ordinary and simple life on Oahu--including hiding her from her svengali grandfather Watari, and the whole Host of Heaven if they can.  To Ryuki's horror they cannot hide her from her legacy--she too hears the Symphony.  He is determined to stay alive and in her life to keep her sane through this, and ultimately to demand to know why this 'gift' has been passed down to her.
In a very real sense, she is his heart.  He would sacrifice his very soul for her, but mostly he sacrifices time, flying frequently "on business trips" to be by her side.

Kahuna
Hawai'ian beachcomber, surf instructor, unofficial truancy officer, and priest of Pele
Kahuna found yet another kid ditching the boarding school on Oahu, younger and more homesick than most but otherwise just another kid ditching school.  It was Kahuna who unravelled the mysterious music that haunted him and assured him it was real, and that he was not insane.  Kahuna, unimpressed by his by-then diminishing psychokinetic tantrums, he was one of the first adults to treat Ryuki as though he were nobody special.  
He sent the young kid up the mountain for his inititaion--the climb to break his anger, the sacrifice to test his compassion, the goddess to give him fire.  And then, the ordeal passed, he taught him to surf, to remember man's place in the world.
Kahuna is still a dear friend and chosen family, and watches carefully over Ryuki, Grace, and Lei'alani.
Kahuna used to be James Bouchier, a young and foolish man who dabbled in the occult in its heyday, in the 70's. He learned the hard way what a bad idea it was to traffic with demons and ran for his life and his soul, eventually landing on Oahu and discovering 'paradise' there.  

Pele

Fierce but loving patron goddess of Mount Kilauea, she along with her brothers and sisters are protectors of the Hawai'ian islands..  Gathering essence into her volcano from thousands of tourists, spreading her legends throughout the world, she has used this and the islands' unique location to make of Hawai'i an ethereal sanctuary.  Without an Archangel or Demon Prince of the oceans and waters, the islands sit in a celestial void,and any celestial who visits is gently nudged away.  The drawback is that this void is like a silence, magnifying any disturbance that is made.
She is protective of Ryuki as she is of any mortal who is dedicated to her.   The sole tether in the Hawaiian islands, to her chagrin, is a tether of Gabriel on Mt. Kilauea itself. Fire uses it judiciously, knowing from experience that Pele will drive interlopers into the crater and not care whether they'll go through Trauma on the way off her island.

Bio:

Fledged Ofanite in the year 1145 Anno Domini, Corat was paired with one of a handful of pilgrimage angels. A small brotherhood of Cherubim and Ofanim, these angels accompanied mortal pilgrims on journeys of the spirit, defending them both body and soul on the way. Corat took readily to the mission, eventually distinguishing himself among pilgrimage angels and earning the Master of Motion distinction. He has been to Canterbury, Lourdes, Guadalupe, Jerusalem, and Mecca more times than he can remember. He has also led pilgrims to Plymouth Rock, Lumbini, and Mt. Kailash, maintaining that nonbelievers and pagans are deserving of salvation. Janus, supervisor of the pilgrimage angels, while giving little direction also made no objection to this practice.

In the early 1970's Corat accepted a pilgrimage that no other angel had, to the Shinto war shrine Yasukuni. A Dominican Triad, already used to sniffing around Janus'servitors, followed him there and took exception to the destination. After a brief conversation Corat was hauled to the celestial realm for a trial.

The charges were simple and damning. Yasukuni was an ethereals' shrine, and the pilgrims would be feeding them Essence. (Incidental, said Corat. A small price to save a soul.) It glorified war criminals, suggesting they were no guiltier than their conquerors' judges. It honored women and child soldiers as war heroes. It glorified premeditated suicide as a war tactic. It held that in any war or argument, both were wrong and both were right, a nearly complete moral relativism. Corat denied none of this, without shame. What hurt was that he was forced to give up his confidences, the hundred little things told to him by the pilgrims, the opinions he held that he knew were unorthodox, an appreciation of the virtues of unrepentant pagans. Yet still the Triad was hung, one Seraph for, the Cherub against, the third a Seraph of the Sword undecided.

Michael the Archangel intervened for his own reasons, sending an emissary to speak to the undecided Seraph. Rather than having the desired effect, the Seraph took exception to an outside party attempting to influence a Triad and voted guilty. Corat lost his highest Distinction, some ethereal Forces, and was taken off pilgrimages until further notice, effectively denying him the Word so nearly in his grasp. He was devastated.

Janus imposed on Michael to fix what he had broken, and Michael assigned Corat to train with the Corps. While their purely martial mission was at odds with his nature, the constant discipline distracted him from his pain and strengthened his soul. Kyle, the Cherub he trained with, became a dear friend and Ulysses their commanding officer became a father figure. It was unlikely that Corat would legitimately earn a spot on the Corps, so rather than see him fail Michael pulled him out early. After a brief and recreational mission touring with the Grateful Dead fans, Corat was tapped for a new task.

Frustrated with the progress of the War under Laurence's clean hands, Michael tapped Corat to work a secret project aimed at tipping the balance. He would recruit from among humans the wiliest of soldiers, a dozen or so people from among the pagans, atheists, and other folks Laurence deemed unfit. He would find them, evaluate them, adjust for their flaws, and gently persuade them to work for Heaven's cause. Corat knows that Michael will not readily admit the project's existence, meaning he might well sacrifice his existence in the name of angelic harmony if he is discovered.

Knowing that Laurence and Dominic have become curious, however, Michael set up a second project that Corat could pursue in the open: the Mile Higher Club. While Baron Samedi is in fact a concern to the Host, the project allows Michael to support his servitor openly. Laurence is not quite convinced, sending a Seraph to the team. That Seraph is Shenmachel who, while ignorant of his true purpose there, is by nature pure and devoted and will report any irregularities without asking.

Relations:

Corat maintains a centuries-long friendship with Rina-el, grateful for the comfort and the reprieve from the War and the ability to openly associate with an exotic dancer. Of his recruits he will not admit to a favorite, but he clearly appreciates being able to speak openly to Ryuki. Ryuki discovered his angelic nature on his own, and while he would be offended that he's part of a mission, he's wise enough to know that Corat's interest in him is probably related to the War.

Corat has made friends with Alx Le Dante, a Santa Monica artist without any clear soldier potential. Alx is Corat's tour guide to humanity, teaching him how to better blend in to the modern world. Alx teaches him how to feign interest in women, because as part of his pilgrimage construction he has no erotic urges (to avoid objectifying people.) A bug or a feature, depending on how you look at it. Alx also allows Corat to possess his body from time to time when he needs to be in the air on John Wyatt's day off.

Corat met Jen Breckenridge about three years ago on one of his many flights, and quickly discovered that her son was an Impudite of Dark Humor. Unable to destroy the Imp without throwing Jen into despair, Corat settled into a passive-aggressive battle with the demon Pepito. Eventually he fell into a pattern, taking out his anger at the Triad on the demon while failing to either extract it or destroy it. This inability to break free of their destructive relationship has led to dissonance in Corat, finally bundled into a Discord for claustrophobia.

He has remained friends with Kyle and Ulysses though he sees them rarely. Kyle often teases him that "somewhere out there is a Cherub who can't sit still, because you gave some Ofanite your place in the fledge line."They call him by his boot camp nickname "Teddy Bear" because "He may not be great in a fight, but when he's in the room suddenly everybody feels okay. Still he knows a soldier's rules, that they won't ignore orders on his behalf.

Shenmachel reminds Corat of the Seraph in the Triad, and he's suspicious of him for that reason. He still dislikes Seraphim in general, and servitors of Laurence and Dominic in particular, and suspects Shenmachel is here on behalf of one or both of them. He's not sure, so he's unwilling to confront him.

Zahira's presence comforts him as a representative from Khalid. He's seen Islam's beauty firsthand and appreciates the difference of faith Khalid represents.

The continuous presence of Yves'representatives suggests to him that Destiny may be on to his recruiting mission and intends to participate.

Corat includes on his team whoever comes to him, and trusts the Lord not to send him anyone he can't handle.

He is proficient with a pistol for his role, but his passion and skill are for archery.