First of all I want to say I DO NOT hate Nezuko. I don't even dislike her! I just think she wasn't that well written.
Why I think Nezuko is poorly written: 1. She's just plot armor most of the time! Whenever the writers write themselves into a corner and realize Tanjiro can't win, or they need a filler episode, she comes in. She never trains, she never makes her own relationships, she never dies, she's just the one who comes in and saves the plot. Not saying she's never important, it's just most of the time she's just a last minute "erm actually" for the bad guys! 2. She doesn't have that much of a personality. I get when she was human she had a personality, but the creators made it that when she became a demon she's just...there. Sitting in a box. No voice, no choice, no nothing. She just sits quietly in a box 99% of the time, and when she does come out she can't even speak her mind. It's like there's no thoughts in her brain! 3. She doesn't have her own life. She's always with Tanjiro. She fights the demons Tanjiro's fighting, she's friends with Tanjiro's friends, she's barely ever on screen if Tanjiro isn't. She's just "Tanjiro's Sister" not an important character! And I don't like that! She should be so much more! 4. No struggle! It'd be so much more rewarding when she wins if we actually saw her train. It's like she just woke up and got a notification saying "Yo you conquered the sun!". She's too OP. And It'd make her so much better if she struggled with eating people. Just sleeping it off is boring to watch, and a waste of writing potential. And I hate that she was hypnotized into seeing everyone as family instead of choosing to. 5. She goes from smol bean to fan service so fast it's illegal. Like wdym she's a toddler and adult at the same time?? That's BEYOND wrong! Choose a side! Okay that's all I can think of. And again, I don't hate Nezuko, I just wish she was less bad OC, and more relatable character. Please don't attack me if you like Nezuko, it's my opinion >:( and I DO like Nezuko too i'm just complaining about the parts I don't like. (Feel free to tell me why you disagree in the comments tho if you don't like what I said)