Full Kanon and Clannad spoilers.
So, while I was making the image below, I realized something; obviously, Ayu and Fuko’s routes share the same skeleton. But why? Once upon a time, I put in the back of my head as Maeda possibly honoring Hisaya as a writer following their companionship from Kanon (a theory I base on absolutely nothing) but then I wondered something. What if Ayu and Fuko aren’t different. What if, and bear with me here, they’re the same person? Anyone who’s seen a time loop in fiction can tell you, reality is only what our small brains can perceive. Kouko claims Fuko had been in her coma for seven years, but I don’t think once it is said that Clannad actually takes place in 2003. 1999, perhaps? Ayu has also been in a coma for the exact amount of time. Both of them are still children. Both of them are the same person.
Fuko comes from a timeline where Yuuichi failed. Nay, the timelines where Yuuichi failed. Fuko is the result of every bad end Ayu, punished for her sins of taiyaki avarice. Further trapped in a time loop, winter ends, and spring begins. Ayu loved nothing and no one, thus is granted someone to take care of. To earn her wings and free her from the infinity loop, God grants her a sister to take of and a home to go back to. Paradise isn’t something given to you, it’s something you create yourself. Yuuichi can’t save her anymore; in the end, Ayu realizes that she can only really save herself. Thus, because she has short hair, she grows it out instead of doing the anime trope of cutting it all off. All she has is a knife and all the wood in Hikarizaka’s forests. Ayu died that day, because of the wind. Then, Fuko (wind child) is born.