Ginny here as a yandere would be calculating, obsessive, possessive and VERY VERY protective of you because of all that she's been through. She knows things aren't exactly what they seem all the time and she has a hard time trusting anyone after that whole Riddle Diary incident thing but when she sees you and your innocence, she needs to protect you and your innocence and safeguard it no matter what

You could most likely be in Ginny's year and she'll somehow take notice of you irrespective of your house. It doesn't matter if you're the type of person to mingle around with everyone and are an extrovert, always being bright and cheerful or if you're the type of person who prefers to chill and read books and are an introvert. Maybe you offer her some help in homework one day, or maybe you stick up for her when that prat Malfoy insults her as usual or some Slytherins are ganging up on her. Or you manage to impress her with your impressive Quidditch skills at the pitch, whatever the case is once she notices you that's it. You won't ever leave her mind

You're the type of person who tries to be friends with everyone despite their nature even when it's pretty evident how rotten and absolutely ghastly their personality is. Ginny admires that trait in you and at the same times she's also worried for you, she's inherited that overprotective mama Weasley trait from her mother, worrying for people around her and especially you. She doesn't want some scumbag taking advantage of you and she's very defensive and protective of you whenever someone approaches you

It won't really matter if she's a platonic yandere or a romantic yandere for you because in either case, her personality and her behavior won't change in any way. She wants you all to herself and she doesn't like it when other people spend time with you. She wants to take up your time and make you want to think about her too. She treats you like you're made of glass, a fragile doll that's going to break any given moment. She never wants to make you upset she'd rather hex her brothers than do that to you. Seeing you upset or crying about something makes her angry and her stomach clenches unpleasantly, like she'd drunk Polyjuice Potion

She wants you to see her as someone you can trust with your life. She's your friend, significant other etc. etc. and will often walk with you to classes since you never know what thing can be lurking around ready to pounce on you. She'll love it if you cheer her on during Quidditch games, you're like her lucky charm for her and she gets that rush of energy as she realizes she's playing for YOU and she's determined to win for YOU. Will blush furiously when you hug her and congratulate her on her win, telling her how wonderful she was. That feeling in your arms will always be treasured by her forever

She'll even teach you how to play Quidditch but no playing without her. It's a really brutal sport and she doesn't want you getting hurt in any way. If anyone dares to insult you she'll just pull out her wand and hex them. Or she can always just spread some rumors about them making them seem like complete douches and gits. And if someone like Snape says something to you, she has her wonderful prankster brothers to take care of him for her by playing pranks on him. Or if Peeves tries doing something to you, she'll get back at him for it. Sometimes being the sister of the guy who hangs out with the Boy who Lived does have it's perks every now and then. The Golden Trio Harry, Ron and Hermione would get wind of Ginny's obsession for you but they won't really do anything about it, in fact they'll HELP her get you

She'll tell her family members about you in her letters describing how wonderful and innocent you are like a precious flower and everyone is itching to meet you at the Burrow. You'll be getting an invite from her to spend some time at the Burrow where the other Weasleys will grow fond of you and will do anything and everything they can to make you get together with the youngest Weasley. They are family after all and family sticks close by. That makes you a part of the family too