Why do the leaves turn red when it's autumn?

Hey, Dai-chan.

Cirno believes in me!?
I can't say I don't know.

Since I'm an idiot, I don't know why, but you should know the answer to it.
I have my beliefs in you, Dai-chan.

I don't know that ei-...

I see!!

I've convinced her!!

When trees have fallen in love with autumn, they will turn red.
That's why when winter comes, they become lonely and wither!

Let's at least tell her a white lie, Dai-chan!!

Stooop!

Ah, the goddess of the red leaves is here just in time. Let's confirm it with her.