Seeing Mari and Kaori makes me wonder if the mangaka was inspired by the side couple in Adachi to Shimamura.
Both couples are childhood friends.
Both couples feature an ojou-sama spending time with a somewhat airheaded girl as a much-needed breather from the rigid obligations of her wealthy household.
And for whatever reason I'm just not a big fan of either couple.
I eventually started speed-reading their parts in later volumes of Adachi to Shimamura.
Not that I dislike them. I just don't find them as interesting as the other characters.