????

Japanese girl asked the knight to sleep with her for children, no romance involved, he refused because duh, but then his wife forced him to do as the Japanese girl asked, because she felt guilty about the past, she felt guilty for "taking the guy away" from the elf girl or something. Very weird stuff full of guilt and obligation

She wants to have children to inherit her dojo, but since she already gave her heart to a certain someone, she doesn't want to get married. She also wants to leave descendants to always be there and be a place for MC to return to, since MC is surely living past several generations.

So she asked for the couple's help. It sounds weird and I'm not sure why she chose them instead of some random guy, but I think it's because she felt like they "get" her intention. The couple hesitated at first, but they have their own ghost, which is their relationship with their ex-member, the female elf. So they get the feeling of regret. That their friend drifted away from them because she can't bear to see them dying before her.

There's no love, there's no bad intention. Is it right? Imo no, but they decided to do that, so that's their decision.

The reason she chose to ask him specifically was due to him being a strong sword man and the master of another sword style. He had been one of the other people besides the MC to help her in her journey to start her families dojo again.

The reason I think that she didn't pick a random guy is because of the genetics thingy that when you believe that the female is a good swordsman and having a child with another great swordsman is having a genius kind of child. And you're right she did that because she doesn't want Aesir to be alone and always have some place to go back to.

Yeah, that was such a weird thing, but ultimately their decision. What really irks me is how with that they ended up binding MC to them morally. Like that's emotional/moral kidnapping. Now MC feels a responsibility for Kaeha, because he feels he did this to her because of what he said, when in reality, she just went and did it on her own. In her farewell letter she even asks him not to forget her for as long as possible which is even more selfish. I can't like her because of all of that.

That's the part of the manga I don't like the rest is fine

Yeah, the rest is fine.