King Raynar chose for his wife the daughter of the king next door, the beautiful Princess Raina.
Her sister, Princess Sunna, was jealous and went to a sorcerer, who put a curse on Raina that if she did not ride straight across the stream between the two kingdoms, it would rain there for the rest of her life.
When Raina reached the stream she was determined to cross but a bird flew up, startling her horse so she reined it in.
It started to rain right away.
So, you see, it rained in the reign of Raynar when Raina reined.