Harry Potter and the Order of the Phoenix:
This is only the beginning of the blossoming relationship between the two. Ron actually manages to control his temper, whilest Hermione grows more frustrated with the fact that Ron is still clueless about his feelings. Not to worry because there are even more kicky moments, now that Ron and Hermione are both prefects, and Harry lands himself in more detentions than all his 4 years combined, and just because.
Harry Potter and the Half-Blood Prince:
This book is by far the most romantic one of the six. Ron and Hermione's relationship even furthers its' progress as both of them are seemingly more open to the idea of a relationship with each other. But just when they reach their breaking point, the secret that Hermione kissed Viktor Krum two years before, is heard by Ron, so he decides to get a sort of revenge, and kisses Lavender Brown. And kisses her, and kisses her, and kisses her, until Hermione sends a flock of yellow canaries after Ron in her outrage. Though, by the end of the book -after a terrified Hermione finds out about Ron being poisoned and Ron uttering a special name in his sleep- at the funeral of a...