I read this recently and it reminded me so much of Yotsuba, the main character is a cute cheerful girl with green hair, there's no real plot and the chapters are mostly daily life stories, it also has beautiful backgrounds with a lot of attention to detail.
It's about a robot girl who takes care of her owner's café while he's out for unknown reasons, it takes place in a post-apocalyptic setting where the human population has drastically reduced and the sea level is constantly rising and cities are slowly getting sunken. Despite this, people seem to have learned to live with it, but it can be a bit depressing at some points. Mind you, this manga presents a lot of mysteries, but it answers almost none of them.
This manga has two OVAs that adapt some stories from the manga, the first one is beautiful, but you can skip the second one.
I also learned about YKK from this board (or one of its past incarnations) and I found it quite enjoyable, so I second this recommendation. I liked the OVAs too.