#read with caution

Based on the Italian publication write up (if translated correctly), Emma is deaf in one ear. And the casting call for young Emma states she doesn't fit in, is a loner and developed a peculiar fixation.

There's also a near 10 year age gap between the characters.

My guess is Emma was bullied by one of Charlies young relatives growing up (maybe younger sister or brother), and Emma is a school shooter. Maybe she doesn't go through with shooting up the whole school, but somehow still shoots Charlie's sibling, killing them. Or, Emma played a psychological number on the kid and caused him to cause his own death.

Whatever happened during that time (an errant gun going off too close to her face, or getting hit by something, like a rock) caused Emma to lose her hearing.

That's my theory

Years later, Charlie and Emma meet, none the wiser of their connected past, fall in love and the secret slowly starts revealing itself, culminating at the wedding reception.

Or, plot twist, Charlie's relative gets blamed for a school shooting Emma caused, ruining that person's life.

Riddle

Possessive.

❥ If the red-haired leader doesn't enjoy it when his own dorm students break a rule or disagree with him, imagine what it would be like with his beloved.

❥ Forget about trying to make a decision for yourself again, you don't need to do that, sweetheart. Riddle will tell you what to do, how and when. It will be completely up to him from now on. Whether you like it or not.

❥ The king of roses won't let you lift a finger; his delicate lady shouldn't even be in contact with other people. You only need him. He is the air you breathe, the light that guides you, and the water that flows.

❥ Don't object, or it will be worse for you. Threats to your own integrity will be the order of the day with this guy, and if he gets angry, he won't hesitate to be harsh with you. After all, he has to educate you.

❥ Poor you if he finds out that you have become friends with another student, because he will not hesitate to use his magic twice to decapitate them. No, we are not speaking metaphorically. And if he so desires, he will bring her to your bed with a large golden bow adorning your gift alongside a rose.

Ace

Impulsive.

❥ Ace is a capricious boy who will get everything he wants, no matter what. He doesn't care if you're against his wishes. Because, to him, you're already his.

❥ His cheerful face mixed with the idiocy he shows to other people is what makes others believe that he's not someone to be feared. When in fact, he's quite the opposite.

❥ Trappola is completely unstable when it comes to his affection; at one point in the day he could be hugging you, like the fallen angel Lucifer once was, and five seconds later he would have you on the floor against your will, with his magical pen pointing directly at your throat because you walked away from him to get some water.

❥ But don't worry too much; if he's the one making silly jokes and pranks, you'll be safe... But don't you dare try to make him laugh, because if he misinterprets your joke or you talk about someone else, the redhead will completely change his mood.

❥ Even so, being a Yandere, Ace is completely honest with what he says and thinks. If he tells you he's “hungry,” it's because he is... If he mentions that he “broke someone's neck,” well, we're going to have to dig a hole. No lies.

Deuce

Dependent.

❥ Deuce is a type of Yandere who likes to be attached to his beloved all day long. Forget about having a moment alone again, because he will always be there; he will send you a message, call you, and find a way to stay by your side in and out of class. So he will be in your dorm room every day of the week.

❥ Even so, he behaves like a little puppy eager for the attention that only his beautiful girl can give him, whether it's a kiss, a pat, or a gentle hug. He'll always be behind you asking for your love.

❥ He can be suffocating, but he swears it's because he loves you and doesn't want anyone else to have a moment alone with you.

❥ But of course, not everything is going to be sunshine and rainbows with this guy; after all, he has his dark side. His emotions are completely unstable; he can go from tears because you refused him a kiss to rage in less than a minute.

❥ He doesn't want to be alone, so you're going to be with him whether you like it or not. It doesn't matter if you die in the process; that will only make the idea of being together easier.

Trey

Delusional.

❥ For the vice leader of Heartslabyul, you've been his partner since the moment you were kind to him, no matter how many times you've rejected him and emphasized that you're nothing to each other. He doesn't understand, he thinks you're just playing games... And that's really sweet, that's why he loves you!

❥ He's going to look for you. You're dating after all, in his twisted fantasy. He'll always be there for his beloved. Whether it's in the morning or in the middle of the night, he'll try to be there to take care of you like the great boyfriend he is. Oh? Did you slam the door in his face? It doesn't matter, dear, he knows you're shy.

❥ There's no way to escape the mental lie he created, you can only try to hide and pray to any deity that he won't find you. But that would make your precious partner really sad.

❥ That day you tried to run away from him, you saw the grotesque side of Clover, but believe me, the only way to keep yourself protected and truly loved is with those ropes on your legs and hands. All lovers do that, don't they?

❥ He's a completely changeable guy, sometimes he'll want to break your legs so you can't run away from him, and sometimes he'll make your favorite dessert as a surprise gift. Whatever his beloved desires.

Cater

Fan.

❥ Heartslabyul's playboy is someone who catches the eye, seeming to shine wherever he goes, but then why doesn't his beloved see him? He has a paranoid syndrome, believing that everyone always pays attention to him, everyone except his beautiful, perfect one. And, unfortunately, he only wants her gaze on him.

❥ And he found a way to make sure your eyes saw him, that your mind thought of him and no one else. Your eyes gave him your full attention when you got upset with him for dirtying your pretty uniform vest. That day, in Cater's mind, a brilliant idea was born.

❥ From that moment on, the Yandere didn't stop bothering you. Things that started out innocent and without bad intentions twisted to the point of desperately searching for you in the hallways just to pull your pretty hair.

❥ The trouble began the day you didn't continue the game, the day you stood still, didn't scream, didn't cry, and didn't even look at him. That just drove him crazy.

❥ His pulling became more violent, and you didn't react until his fists began to hit your skin. You had made him angry, but he didn't stop. Your indifference was a thousand times worse for him than his blows.

❥ He loved to see your lips bleed, feel your body tremble, and watch your eyes, the ones that now looked at him, fill with despair. Now he knew you existed, and that was all that mattered to him.