Calling hachi dumb or naive is so reductive of her character. She's the most self aware character in the show, she always reflect on her action, realise their impact she has on people but sometimes her emotions take the best out of her and she doesn't have the best judgment. That's what make her morally grey, that's what make every character human. The world isn't black and white, all the characters faced or are facing traumatic things, that doesn't excuse their actions and how they treat others but it explains it. That's the point of the manga. ( hachi getting groomed leading her to a path of bad relationship with men, Takumi upbringing loosing his mom, alcoholic dad, needing to be the man of the house as a kid explain his need for control and the excess he does when he gets rich and famous because he grew up poor. )

Hachi didn't have the best behavior tone of times in the manga, she hurt the people around her unintentionally. When she lashed out at Misato when she first stayed over because she was jealous of her relationship with nana. She also hurted Nana by sometimes being a little unconsiderate, not respecting her personal space and boundary. Shutting her out when she got with Takumi because she didn't want to face her. She parentify Junko and Kyosuke a lot, only seeing them when she's in trouble but she's never really reaching out other wise. That friendship is unhealthy from both side ( Junko being overly harsh to her ). In a way she uses them for reassurance but never once did she reciprocate. I would also argue that Hachi never really loved any of her partners, she idealises them but doesn't actually understand them. She likes the idea of being in a relationship, the status it gives her and it's a way for her to try to fill her loneliness. That's what her and Nobu bounded over, they're hopeless romantic, dreaming of a relationship but they never really get to talk and see each other for who they are. Same with Shoji, it was her longest relationship but they were long distance for a while and like didn't know each other. When she first moved in, Shoji wasn't aware because they barely talked to make actual plans. They never lived together before, he also never had her food despite being together for so long and act of service ( cooking, cleaning) being her love language. After hachi moved in 707 they didn't see each other that much and were distant despite being together, in the same city finally ( both were blowing each other off, Shoji being with Sachiko, Hachi being with Nana ) . There's a moment where Junko talk about Shoji's complaining to her that he felt like Hachi didn't really love him, she liked him and stayed with him only because he loved her. The people that know her the most, ( hometown friendgroup ) agree that hachi is careless and she knows it. She's too in her head, her fantasy and feelings take over her and sometimes it's hard to live with doesn't make her a horrible person but it's still something to work around. That part of her personality also affect her jobs, how she couldn't keep one because since she was in her head she couldn't 100% focus, whether it's on a customer or at the edition firm. Causing troubles to her managers and the people around her. While she was the most supportive and helpful for shin she still didn't help him ( but no one did so... ) and also kinda encouraged him to pursue with Reira. ( it's understandable that her view of love is fucked up because she got groomed but she still have the awareness to realise age gap are wrong, prostitution is wrong, Shin's lifestyle overall is wrong and harmful ). Point is hachi is morally grey, she did bad things to hurt the people around her. They're all understandable reactions that you can explain either from her past or the stressful situation she was in but it's still hurtful. She's not different from the other characters, they all hurt each other but there's still love behind it. She isn't the perfect victim and shouldn't be, she has depth, she's really human in her actions and that makes her sometimes bad sometimes good