I don't particularly like her either, but she's not *entirely* useless. She did help a bit when they were in the dungeon, especially in the boss fight with Yoru, and she also proposed the idea that Akira and Yoru to make a pact so they can leave the boss room. Sure, he could've just killed Yoru to leave but so much plot will be wasted if he did, like meeting the blacksmith. Another point I have is that she didn't really force him to help her with her family problems, Akira(or the dungeon, idk) teleported them to her place, Amelia didn't even want to be there and wanted to just be somewhere with him, not there. It was by Akira's own will to help Amelia clear her shit up. About your point about them being hypnotized, her father was gone for years so she can't talk to him, everyone is hypnotized so she can't turn to anyone since they're you know, hypnotized. Another point is she isn't weak, she even helped a ton with their fight with Yoru. But she only helped, she can't solo a damn demon like in the recent chapters (chap 29-30).
About her going with Akira despite only knowing each other for less than a month, is because of trust and also, dept. He fucking helped her fix the whole family affair thing and she just gonna leave him alone after that? She really trust him and has feelings for him(I think?) So it's pretty clear she's going with him. If I missed a point, I'm sorry, I don't really care much about Amelia so I may have missed some points. ╮(￣▽￣)╭
Wow Amelia is so fucking useless. Also she's literally creepy?? If it was the other way around people would have called it creepy but since she's a girl its suddenly okay to kiss a sleeping person without permission and get in bed with him?? She's been nothing but a fucking neucense this whole manga and even got Akira involved in her family affairs that he had nothing to do with.
I'm not sparing that fucker either. Is he a simp or what? How does he even feel about her because it's confusing. The only genuine excuse for taking her along was because of her skill. He knew she would very well just be in the way the whole time and has said multiple times that he preferred to be alone. But what kinda pisses me off is that Amelia supposed to be powerful since she's literally a high elven princess and possibly 100 or more years old but she's still super fucking useless and got kidnapped, effectively getting in the MC's way and causing him more problems.
A Kira's personality is also super vague and we only know a little about him. Atp we know more about Amelia than Akira when he's literally the main character. Her background story was far more developed but her personality is complete shit. She's acts like a self-loathing child and never actually tried to bind with her sister either. She didnt try to clear up the misunderstanding or talk to her father about it and just assumed they all hated her when it was pretty fucking obvious they were hypnotized. She basic forced her problems on to Akira and made him fix them and then forced him to take her along while knowing she would get in the way. In all she's a spoiled fucking brat that doesn't think about anyone but herself. She finally got her twin back and then just decides to leave and follow some dude she met in a dungeon only a few days prior?? Sighhhh smfh bro