Rainpaw was named after Blizzardstar's mentor, and Rainpaw's father, Rainmist, who they look eerily similar to. The original Rainmist died before Rainpaw was born, and sometimes Blizzardstar swears that he can hear Rainmist's voice from Rainpaw's mouth,

​

Rainpaw is… odd. They have conversations with the wind, and whisper to the stars. There is something intrinsically different about them. They see things others don’t. Cats tend to stay away from Rainpaw - who wouldn’t, especially when their deep insight is turned onto you, specifically. Imagine, an apprentice, barely out of kithood, being able to look at you and simply know. What they know is often unknown, but the comments… Rainpaw’s comments are disturbing.
“Listen to the star’s advice. They know what you will need when the time comes.” "Listen to your instincts, because winter is harder if you are not in tune.”
“Notice… hear the wind’s secrets, they will help you face it.”

“Make sure that you listen to our leader. Blizzardstar will help you. Always.”
Rainpaw is not magical, or prophetic. Simply odd. And possibly helpful. In fact, undeniably so. 
“Tomorrow the skies will fall,” simply means that it will rain.
“The stars tell stories,” the stars allow Rainpaw to know their way around the tribe’s territory, each pointing them in the right direction.
“The wind whispers secrets,” yes. The wind - temperature and direction - suggests to them what the weather may be.

All of Rainpaw’s behaviour has an explanation - heightened perception. They simply do not know how to show it.

They are, admittedly, insecure about themself. They try to be helpful, that is all they really aim for, but don’t quite know how to show that without the cryptic comments, and mystical phrases that mean everything to them, and nothing to others. The looks that they receive when they speak, the subtle movement of parent’s in front of kits, protecting their young from the odd kitten. They sting and each comment alienates Rainpaw further. It hurts. 

Why them?

Rainpaw doesn’t understand. One day they will. Perhaps one day they will manipulate themself to fit in with the tribe, to become perceived as normal. Perhaps have their behaviour as a kit joked about. Mocked, even. 
(( "Do you remember when you would make prophecies and scare everyone? You were so odd.” ))
and Rainpaw might want to hiss back unsaid words, stuck in their throat. 
(( "I still want to talk like that- I still want to help like that. Let me place crushed berries outside to help the beetles, let me place straw in certain spots so that birds can make warmer nests. I want to place seeds from the barn near mice nests in winter, because otherwise they’ll starve- I just want to help.” ))

But not now. Now, they do not understand the subtle social structure of the tribe, do not understand how “normal” is something that they do not fit the definition of. They are not contend to be odd, certainly not, but they don’t have a choice. They just want to help.