It feels really strange starting the comments thread for a yuri manga...
These are really, really good.
They are all about relationships. About coming to realize that what you feel for your beloved is real and true, even if they are the same gender.
When it comes to the heart, gender can be irrelevant.
Concerning story arcs 1-5: It's an interrelated series. It really is best to start at the beginning and read through to the end, as each story arc builds upon the previous arcs.
The afterward is the author and artist's comments.
Her is independent of the previous story arcs, although set at the same school.
While there are sections where they post "mature content ahead" warnings, there is nothing graphic that occurs, not really. Just enough to make it clear that, yes, they have moved beyond a platonic relationship. Or that they are actively hoping/planning on moving beyond a platonic relationship; some imagining does occur.
There's one code that I'd dispute: Comedy. Yes, there is humor. But, these aren't what I think of as comedies. Nothing is played for laughs, not really.
There's another code I'd add: Romance.
This is a collection that I plan on recommending to my sister and sister-in-law.
Actually, if my parents were still alive, I'd have no qualms recommending it to them, either.