Deku is the most delusional yandere you have ever met. He is controlled purely by delusion and he believes one hundred percent that you are meant to be together. In Deku's mind, he is your hero and you are his princess. And a hero needs to protect his princess! So Deku will protect you no matter what! And if that means he has to stalk you, kidnap you, or kill anyone who gets in his way then so be it. He'll do anything for his love!
As sweet as Deku is, he is a very dangerous yandere. He is hardworking and will never give up, no matter what! His fantasies of your life together keep him going and anyone who gets in the way/attempts to break his delusions is quickly going to end up on this yandere's bad side...and you don't want that, do you?
No, no, you only want Deku to love you!
Meeting You: When Deku meets you, it's love at first sight. He's instantly struck dumb, unable to move or speak or, well, do anything besides stare at you. All at once, it's like the rest of the world vanishes and it's just you and him. You and him. You and him. You and him. It sounds perfect to him. So, so perfect.
"Hey, Deku? You okay?" one of his friends call.
Once he's got his body and brains back, Deku will shyly approach you and introduce himself. And once you smile at him (the prettiest smile in the world!) and tell him your name, well, that's it for Deku. He believers that destiny has brought you together and decides to male you his. Y/N and Deku. Y/N and Deku. Y/N and Deku. Perfect!
"This must be my soulmate!!"
Stalking You: Deku is an intense stalker. And he's good at it too, crazy good. This yandere will follow you around day after day and nobody will ever catch him doing so. The only way you will even know that someone is following you is if Deku begins leaving clues behind (which he might do because he views it as romantic). Deku loves to stalk you, stare at you, follow you around and even occasionally bump into you somewhere (if he's feeling brave or wants to get someone away from you) But he won't just follow you around town or something, Deku is going to do much more then that.
He'll keep notebooks, detailing every little thing about you that he learns. Day to day life, daily habits, favorite things, hobbies, your relationships with others (which he hates), secrets he discovers, who he wants to get rid of, and more. He'll take pictures of you, printing out his favorite and keeping it with him always.
"Ah! Where...where's my pen? I need to write this down!"
He'll break into your home to go through things, taking the time to lay on your bed and write down new findings. He'll take things too, clothing items, small pieces of jewelry, and more. Deku will have a nice little collection of your things back at home, hidden neatly in a box. When he feels braver, Deku will begin to break in when you are asleep, watching you and even laying beside you.
"Oh, you're so beautiful! I could lay here forever and ever..."
When he has access to your home, he'll hack into your computer and phone in order to "watch over" you better. He'll read your text, go through your history, access all of your personal documents. If you are a writer, he'll read and love every word you type.
"Let's see what you're up to, Y/N..."
Deku takes stalking to a whole new level and he sees absolutely nothing wrong with it. After all, someone has to protect you and, as your future husband, it should be him!
"Oh, Y/N..."
His Fantasy: Deku is driven by a fantasy, dream of his. It was born the moment he fell in love and it continues to grow with every second.
In his fantasy, you are at his side, loving and supporting him. And he is at your side, loving and protecting you. The more time that goes on, the more detailed this delusional fantasy gets. He'll have an entire, special notebook just for this fantasy life together.
He plans everything from your very first date (dinner and a movie, always a classic), to the slow progression of your relationship. Deku plans out your first kiss, introductions to each other's families, how he proposes (he even designs the ring himself), your house, your wedding, the family pet, how many kids you'll have (including long lists of potential names), and a million other details that he truly believes will happen. Deku refuses to let anything or anyone get in the way of your wonderful life together.
"It'll be so perfect!"
Kidnapping You: Deku will kidnap you.
He's just so scared of losing you that, in the end, he feels like he has to. You could be madly in love with you and he'll still kidnap you, unwilling to risk it. He's the kind of yandere who prepares for this carefully, choosing a safe house and setting up surveillance inside and out (because he has to keep a close eye on you!). He'll make sure that you have everything you need, even buying your preferred products, and stock up on food (all of your favorites of course!). Finally, Deku will decorate everything in your favorite color and fill it all with your favorite things.
Once everything is ready, he'll make his move.
Imagine waking up in the middle of the night only to see a smiling Deku leaning over you.
"D-Deku?! What are you-"
You never get to finish your sentence, quickly falling back into your dreams. Deku will carry you away, whispering sweet things to your sleeping form. When you wake up, you won't be tied up (unless you do something to make Deku tie you) but you will be trapped in a beautiful bedroom. Here, Deku will excitedly begin his life with you! Though your tears and fighting and begging may upset him (and bring out tears of his own, the crybaby), Deku remains certain that you'll soon understand him...and fall in love with him of course!
"Welcome home! Do you like it?"
Your Relationship: Deku will do anything in order to build a relationship with you.
He wants to be your boyfriend, your true love, your hero. All he truly wants is to be at your side for your entire life, kissing you and loving you. So he'll do whatever it takes to make that happen. He'll get rid of the people who are "in the way" quickly and easily. He'll study you, using every detail to his advantage. He'll whisk you away ("No! Don't call it kidnapping, that's a terrible word!") and keep you for himself, determined to make you love him.
"Love me, love me, LOVE ME!!"
And he just might succeed. Deku is so sweet and loving and affectionate that he has a strong chance of winning your heart. Everyday, he'll become closer and closer with you, giving you anything you want and doing everything you ask of him. Slowly, you'll become softer to Deku and while you won't notice it, he definitely will. You no longer flinch when he comes too close, you smile at him and talk with him more. Deku will be so happy that you are finally falling for him, just like he always wanted! A smarter person would call it Stockholm Syndrome but Deku calls it love.
Punishments: Deku won't punish you in any actual ways.
He doesn't lock you away (he calls that living together, not punishing you), beat you, or anything like that. He is, however, great at making you feel guilty. No matter what Deku has done, he'll always have an excuse for it. His tears and his begging for forgiveness will soon have you comforting him, apologizing to him, begging him to please calm down! Deku, without realizing it, is a master manipulator. Once you start to fall for him, it'll only get worse from there.
"Why would you try to run, Y/N? DON'T YOU LOVE ME?!"
No, Deku won't lay a finger on you. But the things he will do to others, well...An enraged Deku will take it out on those he feels deserve it, especially the people who he thinks have gotten in his way. You can't possibly imagine how brutal a love struck, angry Deku can be unless you have witnessed the violence first hand...and trust me, you don't want that.
"I did it for you!!"
Little Things:
Deku wants to have the perfect life with you. Marriage to the love of his life, children running around and sitting on his lap, a pretty little house, everything. He dreams of it night and day, day and night, and he is determined to make it come true.
"Wouldn't it be just perfect?"
He wants at least three kids (especially a little girl who looks just like Mama!) and would be the most doting Father, even from day one. His kids will be totally spoiled and will most likely become yanderes themselves.
"Come to Daddy! I want kisses!"
Deku loves to dress you up in the prettiest of outfits. They are already waiting in the wardrobe when he kidnaps you and he will just beg you to please, please wear them! He got them just for you after all, don't you like them?
"You would look so pretty in this."
Deku is very easily manipulated by you. He will do just about anything you ask of him, as long as it isn't something like "let me go" or "kick that puppy". But if you ask him to kill someone for you? To get you this and that and just about anything? Well, sure thing!
"Anything for my darling!"
He's constantly complimenting you and calling you his sweetheart, his love, his darling, his soulmate, and at least a hundred other things! And he cannot wait for the day when he can call you his darling little wife...
"Mine, mine, mine! My beautiful lady!"
Deku loves to cuddle with you. Anytime you are together, Deku will pull you into his arms and just refuse to let go. He loves to cover you in kisses and whisper sweet little things in your ear as he hold you tight.
"I love you SO MUCH."
Deku isn't the kind of yandere who can really share. I mean, sure, if he totally trusts and loves this other yandere then maybe...but it'll be hard! He's the jealous type and tends to believe that everyone else is far below you. Sharing is very difficult and he is far more likely to simply kill the other yandere rather then share you with them.
"She only loves me!"
I can totally see All Might (who is also a yandere in this world) having a beautiful daughter and, well, Deku is just head over heels in love! You are protected by your father now but what happens when All Might is gone? You'll need Deku by your side then, as your hero and your husband!
"Please, I love you SO MUCH!!"
He won't care if you use your quirk on him and he won't use his on yours. And if you are totally quirkless, then it will just make him want to protect you even more! In Deku's mind, it'll make him the only one who can really understand you.
"Don't worry, Y/N, you have me now!"
No being a pro hero for you, it's too dangerous. Actually, Deku doesn't want you to have any job really. He says that he will provide for you so you don't have to worry or work or anything as long as you are with him!
"You could get hurt out there! And I can't risk that!"
Deku is the kind of yandere that will never, ever let you go. You can't break through his delusions of true love and he is willing to do whatever it takes to make you his. If you are good, he'll be sweet as pie! If you are bad, well, he'll teach you better then that!