From a family whose blood was so pure they'd been included in the Sacred 28, Julius Selwyn had no reason or intention to sink to even looking at a muggle-born witch, and for 25 years of his life, he didn't. Until that was, he met the Japanese witch Kagome Hakumo.
Their relationship was unexpected, to say the least, but with Julius capable of causing serious damage to the family name his parents made the decision to refrain from disinheriting him with two conditions: Hakumo had to pretend to be pure-blooded, and she had to sign a prenuptial agreement. Both agreed to this, though Hakumo was a little concerned in regards to the prenup, and they were married a few months later when she became pregnant.
11 years and five children later, Julius got home early from his high-up ministry job to find his wife in bed with a man he'd never even met. The divorce was filed as soon as he could get it, citing his wife's adultery as the public reason for the divorce. Privately, he couldn't really care less - he'd fallen out of love with Hakumo years before and had been waiting for a good reason to divorce so he could marry his mistress, Kim Hae-Soo.
The prenuptial agreement saved the Selwyns' family fortune, but there was no such barrier to save Hakumo's reputation. The only thing that stopped her ex-husband from declaring her real blood status was his love of their children. Oh, and his regard for his family reputation.
It caused a stir in pureblood society when, only six months after divorcing his first wife, Julius Selwyn remarried, this time to a pureblood from South Korea, Kim Hae-Soo, who the general public believes he met a week after his divorce. That's not true - he had, in fact, been seeing her for years after meeting her at her fourth husband's funeral.
This wedding was remarkable not only because of its proximity to his divorce but also because of Hae-Soo's reputation in wizarding England: she'd had six husbands before marrying Julius (aged only 28), each richer than the last, and each had died in mysterious circumstances, leaving all their money to her. It helps that Hae-Soo is gorgeous - it's been speculated that there was a veela somewhere in her ancestry, but both she and her family deny this and there's no record of it, so we must conclude that she just got really lucky with her genes.
Cassius and his twin Calliope Selwyn were born a little more than a year after their parents' marriage, the youngest of their father's children and eldest of their mother's. They always suspected they were accidental on their mother's part because in her six earlier marriages she'd never once gotten pregnant and she once told them, aged five, that children were a liability. It's not that their mother didn't love them - in fact, their fairly certain they're some of the only people she loves - it's just a fact. Cassius and Calliope Selwyn were a happy accident. As was their little brother and sister, Carlisle and Pandora.
Oh, and Nathan, but no one's too sure on the origins of his birth really. He was born supposedly in February of the following year, nine months after the twins but no one has any idea what he was real birthdate is. They kind of just pick a random day in February, go along with it if Haesoo tells them its Nathan's birthday, celebrate, and move on with their lives. Nathan, however, was really born in November. Haesoo spent a couple of days out by herself at a nature resort, claiming she needed time to herself to just relax. At this resort, a Siren colony was nearby, just three miles away in a large warm water lake.
When she found the lake, she visited it for the rest of her stay and came home pregnant with the child of a siren she'd never see again. Like she later did with Pandora, she somehow convinced her husband that this was their child despite how quickly she had gotten pregnant again after having the twins. It didn't matter though because Julius fell for it regardless. When she actually gave birth to him in November, she faked the following months of her pregnancy, not allowing Julius to see her when she supposedly delivered Nathaniel in February.
Truth is, he'd been alive and well for three and a half months. Julius hadn't been attentive enough to realize the infant was three months old instead of three days old when Haesoo finally brought him home after having a friend keep him. The twins weren't old enough to remember his exact birthdate, so no one questioned anything, and per usual, Haesoo got off clean, integrating Nathan into their family like he totally wasn't a half-Siren and accepting all the congratulations she got for having another beautiful, healthy baby.
Somehow, Julius managed to survive all the way through Nathan's childhood which was great, Nathan supposed, if he actually had a good relationship with him. Opposed to his mother who seemed to pretty much adore Nathan, he and his father were never on good terms for the whole eleven years Nathan knew him before he died. You can imagine that Nathan didn't spare too much remorse at the funeral. Besides that, Nathan's childhood was relatively spectacular.
Opposed to him now, he'd been a very cheerful and hyperactive child who had a desire to explore and discover. He wanted to see everything, do everything, be everything. To him, the sky was the limit, and as a young boy, he saw the potential in everything. It helped that no matter what he did, he seemed to have an affinity for it. He could literally pick up any hobby and in the span of a week have it down already. He was all over the manor, flying on a broom in the hallways, running through their expansive yard with a kite, rolling down hills and rollerskating to the ends of their driveway. It seemed he could never run out of energy, never stop doing things,
Trying to get him to go to sleep was a nightmare. Not only was he energetic, but he was also an absolute devil child. The servants would literally spend hours tryna to find him or catch him or even confirm that he was in the house. He was quite fond of pranks too, so he'd regularly bother his siblings, bother younger and older, planting elaborate tricks for his own amusement. Ever watched Home Alone? He's Kevin McCallister but multiplied by a thousand. He was cheeky and rude and pretty much caused absolute havoc in his wake.
His first sign of magic was due to a prank going wrong. He was nine and totally thought it'd be hilarious to coat his father's study in bubble gum, invisible, extremely sticky, magic-infused bubble gum. While he was covering one of the desks, one of his siblings, who had been looking for him to call him in for lunch, comes in and startles him so badly he falls into a trashcan which unfortunately had already been coated in the bubble gum substance.
He remained stuck in there for a whole half hour before he heard the footsteps of someone approaching the study again, in which he panicked, triggering his magical blood. The bubble gum became visible and pried itself from all the substances it had been attached to, coiling into a ball and shrinking. Nathan managed to get himself out of the trash can and disappear before anyone ever knew it was him. Besides Carlisle who startled him in the first place, but Nathan got him to shut up about it after some bargaining.
Nathan's first year in Hogwarts was the last year he'd ever truly experience what it was like to really be okay. Soon after the death of his father, a sudden case of depression hit him hard. Everyone believed it was due to Julius' death and he was sent to therapy soon after, but really it was just an offset of chemicals. They'd already been imbalanced long before his father's death, but starting puberty that year had slowly reversed the imbalance, leaving him destitute of happiness for what seemed like no reason. He remembers being in second year and trying to explain to the therapist that it wasn't anyone's fault but his own that he was depressed. In a way, he was right, but it was more due to his hormones than him.
He continued therapy for two years, but when it became evident that nothing, even the anti-depressants weren't working, Haesoo eventually chose to take him out of it, thinking he'd get better with just support from friends and family and a less artificial feeling environment. Nothing really happened. Some days it seemed like it had gotten much worse, and some days he seemed just fine. But eventually, he kind of just learned to co-exist with his depression, even if it was slowly tearing him apart on the inside.