— Born in Monemvasia, Greece to a humane witch (gifted with super strength and self-regeneration) and a mermaid who chose to landwalk for a while and fell in love. Konstantin grows up a small town boy in the ebb and flow of tourists from overseas and honeymooners and thrives on the rich history of his place of birth and learns to fish, sail, and make a living on the sea.
— Childhood's boat gets rocked when Konstantin's mother leaves. As she is a mermaid, the call of the sea is strong and she would rather remain a mermaid than be bound in a human form that is gradually becoming permanent to her. She leaves no note, tells no one, and basically vanishes without a trace. Konstantin's dad tries to convince him that his mother will be coming back some day but he's fairly certain that she's not.
— Konstantin's magical aptitude appeared when he was thirteen. On a fishing trip with his father, he was whistling while hauling up the netting on his own, only to realize that the net was very light. His father had originally thought that it was because Konstantin had inherited his humane plane abilities, only to realize that the fish were practically leaping into the boat. When he stopped whistling, they would return to normal.
— His father sends Konstantin to a magical secondary school on the mainland where he stays with his five aunts and uncles in Athens. He's shuffled between their houses, makes a few friends with the city kids, but mostly just stays quiet and awkward for his secondary school years. He goes back to Monemvasia during school breaks and sometimes never wants to leave, but his father is very stern about him getting a Good Education.
— Secondary school is troublesome. During first year, Konstantin goes through the equivalent of "magical puberty" in combination with his mother's monster blood that runs through his veins. His magic vacillates from harmless and dormant to off the charts and he can't quite get a grip on how to control the tones of his voice. Sometimes he creates pitches that will make someone physically ill, while other times he will accidentally tap into an alluring siren song that creates desirous obsession in the victim. The latter of these two is Problematic as Hell and causes issues between Konstantin and a couple of his classmates (because when you suddenly realize you're in a closet making out with a dude you don't remember being even remotely attracted to that's just. Really weird. And Not Good At All.)
— Konstantin initially doesn't realize that he's doing this to people with the unmonitored pitches in his voice, until he begins to notice this horrifying pattern arise shortly after it starts. It gets bad enough that even plain speaking cuts certain influential patterns into unknowing peers, so frantically, he brings forth the problem to one of his teachers in a fit (scribbling the entire thing down on a note so he doesn't accidentally his source of help as well). Due to this, Konstantin spends two years of his secondary school career monitored, tutored, and quite literally silenced after some investigation and discussion with the administration, his Father, and extended family. During this period, he hones his magic and goes through a number of examinations and testing procedures so that by the summer after his third year of Secondary, Konstantin has his siren song influence fully under control.
— At this time, not only is Konstantin going through weird magical puberty, but also weird merperson puberty (again, thanks Mom). He's developing scales on the bonier parts of his body (knuckles, elbows, knees, ankles wrists, collarbones, hips, etc.) He hides them as best he can with a combination of small glamours and make-up.
— After secondary, Konstantin applies and is accepted into El Colegio de Tomás de Aquino (CSTA) in Madrid, Spain, one of many sister schools to the Barrett-Crowley Reformatory. Undergrad here is pretty simple, though while his magic is perfectly in-check now (with only slight help from a suppression charm he wears pierced into the nape of his neck as a precautionary measure), Konstantin spends it mostly silent save for around a select few people he ends up calling friends. He gets a job at the library (which is one of those open 24 hours a day, 6 days a week type deals) making coffee and filing books into the stacks in his spare time.
— More physical changes happen in uni. During undergrad he's diagnosed with sudden adult onset asthma and scales for days still. He covers them up. A lot. Often. He learns that when he's around blood/meat of any kind, his teeth tend to. Show up. In rows. This is a huge problem so Konstantin decides to go straight up vegetarian to avoid this problem as much as he can. He also becomes a chronic sleepwalker and ends up on the beach some nights.
— Of course, Konstantin still doesn't know his mom is a mermaid until he comes home from four years of undergrad, prepared to go into his graduate studies. He spends the break between undergrad and graduate studies back in Monemvasia with his aging father who is still strong as an ox and lively. That's when he gets told that his mom was a mermaid and all these changes he's experiencing are probably the result of his dad banging a chick(en) of the sea. Konstantin is obviously upset at this portion of his life being kept from him and leaves Monemvasia in a fit because you don't keep secrets for like... your son's entire life (they sort of make up at a later date.)
— He's becomes pretty gr8 friends with a ghoul at a laundromat, named Ash. Why he's there we don't know, but he likes shiny coins just like Kon does so they obviously become very good friends. To the point where Ash literally lives under his bed and steals all the eggs in his fridge and eats all the meat he doesn't want to eat. It is actually a highly functioning friendship, you wouldn't believe it, but it is.
— During this time, Konstantin throws himself straight up into his graduate studies with a focus on honing his sound-related magic (in particular: the manipulation of organic tissue with his voice) and developing it into a stronger and more finely-tuned ability. He can basically hold people down by altering the barely-audible pitches in the air, he can make a person hemorrhage internally, split their ear drums, and break their bones if he's emotionally incensed enough. He starts teaching undergraduate classes as a GA in his spare time, he's working on his magical thesis regarding the human and unnatural plane and manipulating organic tissue, and he's still making coffee at that 24/6 library coffee shop and makes the best latte foam art ever. Talented. Truly. He also finds out that he has a long lost sister that he was never informed about and that's also pretty fucking sweet.
— Eventually he meets one constantly sunburnt dude named Sasha Yelisarov who's like. Kind of okay-looking, he guesses, and seems to look even more sunburnt every time he orders coffee, but like we said, he's kind of okay-looking. Sasha basically comes every day for coffee until he gets the balls to give Kon his number. At first he's like nah but then he's like well maybe okay I think I have a handle on my life and maybe I can go on A Date and not fuck it up completely.
— Sasha is very cute and shy and has a crazy ma who hunts monsters and scares the living daylights out of him, but it's okay. It's fine. Things are actually not bad. They end up really grossly in love and by the time Kon is basically done with school they decide to get hitched, which they're pretty content with. Sasha's mom isn't cool about it tho but that's because she has 0 chill when it comes to monsters and Kon is basically part monster so the only thing that's keeping her from straight up murdering him is the fact that it's actually murder. So.
— Unfortunately, Kon kind of massively fucks up and loses his mind and kills someone in front of Sasha (really. really. violently.) He basically thinks he wants nothing to do with him after that and he's also pretty fucking afraid of hurting Sasha himself so he runs the hell away. Because that's obviously the smart thing to do instead of using our adult words like a person who has a magical graduate degree in Human and Natural magics. Good job, Konstantin.
— Kon goes sailing along the coast of Spain for a while after tossing his phone into a sock drawer at his dad's house in Monemvasia and not even bothering to tell anyone where he's going like an absolute dickwad. He sails aimlessly for a week, not really knowing where he's going. He doesn't eat anything and basically almost dies in a giant storm, but ends up washed ashore in Andalusia off the coast of this tiny town. He gets taken in by a woman named Coralene who nurses him back to some semblance of health, but in doing so, discovers he's half mermaid and is all "son what the fuck have you been doing to yourself" but a lot more eloquently than that.
— Coralene is actually his mother's sister (and therefore his aunt) but she doesn't go telling him that. Instead, she decides to basically beat the beast back into him and release from it's hella repressed cage. Kon is, at first, really not about this plan, but Coralene doesn't actually give him the choice to say no. He's pretty unwell from the wreck still, sick inside, and incapable of healing properly from his wounds because he's deprived himself of all kinds of things natural to his body (all of those things are meat, by the way). He's also hella agitated, his teeth are rotting, and he's kind of In A State. So she keeps him hostage in her bathroom and casts a nasty spell on him that makes absolutely everything he puts in his mouth turn to sand, except for meat 
— Eventually he gives in when she dumps a dead lamb's carcass in the tub with him. I mean like. Why are you going to reject that shit when you haven't eaten anything in ages that didn't just turn to sand in your mouth so he definitely just shoves it into his face and deals with it. Of course, once you pop the fun don't stop so Coralene is kind of relentless with giving him meals only made up of raw meat until he actually starts healing normally again. Funny thing about actually feeding himself properly is that his teeth no longer fall out like crazy and his scales actually (maybe unfortunately) spread a bit more and grow tougher and healthier looking WHAT DO YOU KNOW.
— So basically Kon is forced to accept this portion of himself because it's nice to not feel like crap. He also finds that he no longer feels like MURDERING EVERYTHING, but still definitely believes he can't go home to Sasha ever again. Coralene decides that if he's going to stick around, she may as well show him some mermaid-y ropes like increasing his control over water and air, gradually showing him how to control the ever-rampant storms that are growing quickly along the coast of Andalusia. Eventually, Konstantin begins to master the art of Stormcalling and is able to go with Coralene all along the coastal towns to protect various tiny villages from being washed away from the stronger storms brewing.
— No one actually knows his name as they go from tiny village to tiny village, only that he accompanies Coralene with her storm-carving duties. Over the next few months, Konstantin finds a sense of inner peace he was never able to achieve before. Of course, he realizes that he's a giant dick for leaving Sasha and basically has resigned himself to the fact that Sasha probably would never ever want to see him again (we're going to reiterate this forever). Kon, during this period, develops more. He becomes stronger both physically and magically, stronger mentally, he learns the ins and outs of his powers and the nature of his beast.
— Roughly six months later, Konstantin and Coralene and working through calling lessons on the beach when SURPRISE Sasha is there and Kon is basically the [yeti] emote before the both of them kind of fumble and pull and shove and hug and kiss and cry. A lot. There's a lot of crying. And a lot of Kon apologizing for being an asshole maybe there's even a little getting on his knees and clutching at him because Sasha is his everything okay.
— Sasha basically takes Kon back to Madrid and they kind of gradually mend all the craziness Kon running off caused. He comes back to Ash and to Orla and to his sister, Thea, and basically it's all good for the next few years just prior to The Crawl.
— Just before the apocalypse hits, at the peak of shit going sideways before the true arrival of The Crawl, Sasha's entire family dies Maria's going to make it awful and Kon is just not About That so that's why they're in Alaska. It's a pitstop to Russia. They're gonna basically go get revenge. /fingerguns