Hokuto apparently is a stereotypical rich girl who has nothing else to do but laughing at your face and finding her younger brother a magnet for sexy and ladykiller vets. But believe me, she has much more than meets the eye...

She was born as the eldest of two twins born in the Sumeragi family, one of the richest and more traditional clans in Kyoto, the former capital of Japan. It's said that the twins' mother died by giving birth to them, and when they were little, their father died. So, the ancient leaderess of the Clan, Lady Sumeragi (someone dang knows her first name?! @_@), was forced to raise her grandchildren by herself.

Hokuto didn't have the ashtounding psychic powers her brother Subaru inherited, so Lady Sumeragi declined her granddaughter's option to be the 13^th Head of the Clan. Hokuto-chan never looked grim for it; in fact, she seemed to be relieved by the fact. Even then, Grandmother taught her self-defense tactics (in terms of hand to hand fight she's more skilled than Subaru) and some simple Omjyoutsu (spiritual magic) spells, so she can go by herself in spiritual pinches. Hokuto grew up as a more carefree, liberal, outgoing person than her  reflexive, shy and naive younger twin, happily taking care of him and Grandma, until they moved to Tokyo due to Subaru's work as Oumyouji (spiritual sorcerer)...

In Ikebukuro, while Subaru was attending a case, he had an accident. The person who rescued him was a tall, handsome veterinary: Sakurazuka Seishirou. He also was an Oumyouji, only that he didn't use his skills as actively as Subaru. The three befriended quickly and became inseparable at a drop of a hat; however, while Subaru found himself captivated by this man, Hokuto hid behind her smile and her obsession with getting them together, a dark suspect haunting her...

Hokuto heard from her grandmother that there was a clan of Oumyouji that used their powers to kill people. They were the Sakurazukamori (The Assassin Group Sakurazuka). Anyone with the Sakurazuka surname was, apparently, a member of this clan, and a threat to the person's lives. Lady Sumeragi also suspected that her son, Subaru and Hokuto's dad, fell dead to the hands of the Sakurazukamori. 

The eldest Sumeragi twin tried to brush off these bad omens, but in a moment, the mask fell down. Seishirou lost an eye defending Subaru feom a crazed woman who tried to kill him with a knife, and everything went upside down for Subaru, who realized that he had fallen in love with Seishirou. But when he was going to reveal it, Seishirou didn't only reject him, but told him something terrible.

6 years ago, 9-year-old Subaru found a pink sakura tree, which resulted to be the source of strenght for the Sakurazukamori (in fact, all the dead Sakurazukas were buried under it). A 15-year-old Seishirou met him there; by the law of the clan, he should've killed the intruder, but instead, made a 'bet'. If they met again, they'd spend a year togehter, and if Subaru was able to find out who Seishirou was, he'd live. If not, he'd die. As a proof, Seishirou marked Subaru's hands with pentagram signals, and sealed the memories with a spell...

Seeing his dreams shattered, Subaru retreated himself in his own "muddy conscience". Meaning, he hid his sould inside of his heart, becoming cathatonic, unable to see, speak or hear. His grief was impaled so deep that everything became oblivious to him. To Subaru, there was only the pain of Seishirou's betrayal.

Hokuto couldn't stand such a thing. She had wanted to believe that everything was over, and felt betrayed and hurt too. She knew also that Seishirou would come back soon, to claim Subaru as his prize...

Despaired, Hokuto took the last decision of her life. She'd never let her little brother die; instead, she'd offer herself in sacrifice. Hokuto stole Subaru's Oumyouji garments, dolled herself up with them, and went off to face the Sakurazukamori vowing that her brother would awake someday and face Seishirou himself.

In a Sakura field, Hokuto found Seishirou, waiting. He recognized Hokuto immediately, and she didn't look surprised by it. She said that even when she couldn't defeat Seishirou, she had a spell that NO ONE ELSE could cast. And while casting it...
 

Subaru himself didn't wake up 'til one month later, thanks to an illusion telling him about the terrible destiny that his sister took for him. He vowed to be stronger and defeat Seishirou, to punish him for what he did to him and his family, and take the honor of the Sumeragis higher than any other members of the clan did... So, he quit school and came back to Kyoto, dedicating himself totally to training and his work as Oumyouji, until a certain day in the Promised Year: 1999.