@Shamz Can't really say that for sure. I mean, from a general perspective we would think the same about Yuuji's grandmother, as she's seen to be nothing but irriated with his(grandfather's) behavior, even in flashbacks, but I think to stick it out like she has, she had to see some qualities that she liked about him enough to date/marry and have kids, if
previous mentions are of any concern. In the same way,
she also likes Yuuji, all things considered.
I think the same goes for Chihiro. She does seem to be irritated with some of the things he does, but also sees more and more each chapter qualities that she, in some capacity or another, admires. There are a lot of ways to show love, and perhaps Chihiro can see the attention and care Yuuji places in people to the point she can look past that. Of course, that don't make him any less annoying, but its enough for her to get feelings from.