Quite interesting. Every culture has a folk story behind natural phenomena like the one you described above. You said if it rains then it means that Orihime and Hikoboshi will not meet again for an year. What does the rain symbolize. Is it tears from the lovers or something different?
Afaik it is because they cannot see the way/river to cross when it rains because of the clouds. Nothing to do with the water droplets itself.
I see. So they would not be able to see each other because of the dark rain clouds so they have to wait until the next year to see each other again.
That's right. The rains block the way for them, kind of like an obstacle that gets in your way.