Basic Info:
Full Real Name: So Kichiku
Seishi Name: Tamahome
Seishi Character: The kanji for "Oni" (Ogre), located in the middle of his forehead
Seishi Ability: He was born with martial arts ability
First Appears: Episode 1 of the anime
Age & Birthdate: 17, June 28
Birthplace: Hakukou village in Jusou-ken, Konan country
Family: Father, 2 younger brothers and 2 younger sisters
Height: 180cm --> 5'8"
Hair Color: Dark aqua
Eye Color: Gray/violet

Personality:
From Tasuki no Miko's manga translations, here's what Watase Yuu had to say about Tamahome:
"The oldest son who works hard to support his family in his father's place. An older brother indeed. Because of this he cares about others, and is fequently taken advantage of by people. But he tells himself "What else can I do?" Cheerful on the surface but tough on the inside (I think), is innocent and bashful. This is why he originally rejected Miaka. (For his family's sake he has grown stoic). Will sacrifice himself without hesitation to protect others against any foe."

My own thoughts:
Tamahome is so very sweet! I find myself waffling back and forth between being disgusted at his behavior (the poor boy is whipped, folks) and wishing I could find a catch just like him. Today I'm feeling generous and leaning towards the latter, so keep that in mind when you read the rest of what I've written ^_~.

Family man?
When we first meet Tamahome, he comes across as a pretty self-involved and greedy guy -- though a good looking one. This is actually how Miaka describes her first encounter with him in her diary (that's only in the manga, though). Tamahome's the master schemer and truly knows how to make a buck (or is that ryu?) on just about anything. He would make a terrific telemarketer or door-to-door salesman if he were in this world, don't you think ^^?
Anyway, it is soon revealed that Tamahome's motives and obsession with money are hardly selfish. Left motherless at the age of 12, and practically fatherless as well since his dad was bedridden with illness (though his father is a great source comfort and strength for him), Tamahome was forced at a young age to take on the responsibilities of the household and the rearing of his four younger siblings, particularly his tiny sister Yuiren -- who was an infant when their mother died. His entire focus in life became the safeguarding of his family.
With a little bit of schooling -- but not the right training to really run a business or anything -- Tamahome struck out to raise money for his family the only way he knew how; mercenary-for-hire jobs, acting as a personal bodyguard, and the like. It's hardly dishonorable work, we must admit. I mean, he could have become a prostitute or a pimp or something.

In time, however, as he interacts with the other shichiseishi and gets closer to his love and his miko, Tamahome finds more to live for than just his immediate family; he now has Miaka and his duty to help her summon Suzaku. With his father healed by Mitsukake, and his new challenges in life, Tamahome begins to let go of his obsession and balances it with his other obligations. Now, it can be debated that he becomes a less interesting character once his focus is more directed towards Miaka, but that's a whole other kettle of fish, now isn't it?

I find it a little humorous that Watase-sensei described Tamahome as innocent (see above); personally I think he's slightly perverted (but not any more than usual for a 17-year old guy, come to think of it). Of course Miaka always provides him with plenty of ammunition (can you say "fan service?" I thought so).
Still, for a boy of his age to decide that the most important thing in his life was his family -- and that therefore he would not allow himself to become distracted by things like, oh, say, women -- well, that's pretty noble in my book. That's why I like the little bugger ^_^.

On his relationships with the other characters:
Miaka
Of course, Tamahome's love for Miaka is a given. You could see this relationship coming a mile and a half away (they're together in the opening credits for crying out loud -_-;). Far from being simply puppy love, the relationship between Miaka and Tamahome has stood through many, many trials and tribulations, as well as many hits and many near-misses. Sure, maybe you always know they're going to get back together in the end, but sometimes you wonder just how they're going to manage it.

Hotohori
The friendship between these two is a little strained for the first half of the series, by Hotohori's own love for Miaka. These feelings have resulted in more than one clash between the two seishi. Fortunately, Hotohori eventually comes to realize that Miaka's heart belongs only to Tamahome and he does try to back off. So things soon settle down and Hotohori and Tamahome finally become more like friends, though if I recally correctly they never become terribly close.

Nuriko
Tamahome sees Nuriko as an older sibling (brother, sister, you fill in the word here), and Nuriko in turn mothers Tamahome, as he does all the shichiseishi. I think Tamahome needs the "older sibling" figure, as all these years he's been taking the role for everyone else; I mean, who does Nii-chan go to when *he* needs help and comforting?
Nuriko, on the other hand, relishes his role, and excels in it, since he is by nature very protective of the ones he loves.

Tasuki
Oh, sure they fight, but you know who Tamahome dreams of at night. ^_~;;
I'm just kidding, of course. Tamahome and Tasuki had a rather unfortunate first encounter, and although their friendship surpasses the differences of the past, it also provides them (particularly Tasuki) with ammo for a good ribbing from time to time. The two brawl like brothers, and everyone around them can tell that no harm is meant to either. We all know that when push comes to shove, Tamahome's got Tasuki's back, and vice versa.