the immortal Miss Sumeragi
All that can be objectively said about Hokuto could fit on the back of a postcard, to be quite honest, due to our being given so little information about her early life, or indeed any of her life before the single year's glimpse of her we're given that is Tokyo BABYLON. It is canon that Hokuto was born in Kyoto on February 19, bright and early at 6AM on the dot. Her little brother followed her into the world nearly six and a half hours later; due to this time difference, the twins have different star signs -- Hokuto is an Aquarius, while Subaru is a Pisces. The twins lived in Kyoto until they were eight, when they moved to Tokyo. Absolutely nothing is known of the twins' parents, although we do meet the their grandmother, the former head of the Sumeragi clan, who Hokuto doesn't really have the highest regard for.
We know that both twins were trained to become onmyouji, at least in their very early youth, though unlike Subaru, Hokuto didn't show much aptitude towards magic -- or, at least, she didn't have the dedication towards it that her brother did; she has a few basic spells in her arsenal that she can use when she's in a pinch (and has the nouse to create kekkai with nothing but a Chanel lipstick and her own willpower), which may indicate that the difference of talent between twins is purely a matter of application. As proven by Seishirou's death in X, Hokuto has enough magic skill to enact a killing curse of her own. Her magical intution is very finely tuned, as well. She knew all along that there was a large chance that Seishirou could be dangerous; she states she can smell the blood on him.
Hokuto has been shown to have a deep abiding interest in fashion. She creates all her own and Subaru's outfits and never misses an opportunity to go shopping. For Hokuto, fashion is self-expression; perhaps it wouldn't be too much of a stretch to refer to her as an artist. Her looks are loud, stylish, elaborate, highly creative, at times utterly impractical, and oddly ahead of her time -- some elements of her clothing seem to be from future trends. For example, her EGL-esque look in the beginning of the second TyoBABI OAV, which was released many years before its initial explosion in Tokyo!
Aside from fashion, Hokuto is quite knowledgable about Western astrology. She claims that it's only normal for her to be well-informed of current events and trends, as she is an Aquarius. Hokuto enjoys cooking immensely, and is very good at it. Her ultimate goal? To become a housewife. I won't even get started on the how the simplicity of that dream is compounded by the utter tragedy of her ending...not here, at least.
Hokuto is confident, extroverted, brash, playful, and the very obvious yang to her brother's yin -- the Sumeragi twins are living onmyoudo. She wears her heart on her impeccably decorated sleeve, and is unfraid of doing so. Hokuto knows and lives her own truths, and stands by them. She has few of the usual prejudices most young women of the 90s usually had -- she is surprisingly broad-minded, feeling that the quality of a person's soul is more important than their social position or reputation. This is shown in her encouragement of Subaru and Seishirou's same-sex romance, and her simple decision to become a friend to the girl from overseas -- an illegal gaijin -- in Volume 2's annex, Smile.
Hokuto is beautiful, which is stating the obvious to anyone with two eyes (or one...and that is a very tasteless quip to make on a page for a CLAMP character...). She is physically beautiful, but what makes her shine is in her bubbly personality, her love of life, and maybe even most importantly, her outlook -- one of purest hope. Despite its initial cheerful sheen, TyoBABI is, essentially, a story of despair. It's the story of a fragile boy's hopeless love blossoming for a man who didn't truly exist, in a city that is descending into destruction. Its ending is heartwrenching, but hope against hope is sewn finely through the narrative in the form of Sumeragi Hokuto. She knows the darkness -- Tokyo's, Seishirou's, even Subaru's -- and she smiles at it. She believes in the best of all people and situations. She gives up her life knowing that there is every chance that Seishirou may try to kill Subaru...and she chooses to believe that he won't.
Perhaps the greatest heartbreak of the story is that she was wrong. Or, rather, that she was wrong in her actions but right in her belief that even the Sakurazukamori had a chink in his heart that her brother's own light could seep into. Will it bring any peace for Subaru? We can guess, but we won't know for sure until CLAMP ever decide to finish X -- which I'm not holding my breath waiting for, believe me. Maybe the most painful thing about the trio's whole interconnected story is that we may never truly know the depth of Hokuto's sacrifice, and thus her hope.
Which is just about the most CLAMP thing ever.