Alyss: grey eyes
Annabeth: grey eyes

Alyss: blond hair
Annabeth: blond hair

Alyss: name starts with "a"
Annabeth: name starts with "a"

Alyss: Will Treaty(main character)
Annabeth: Percy Jackson (main character)

My conclusion:

What if Annabeth were actually Alyss and Percy was actually Will? Read my Percy Jackson/Ranger's Apprentice crossover to find out. It'll take place during book 12 of the RA series and many years after the Gaea war. (Obviously. He's, like, fifty or something in the 12th book. I mean, he has a beard and says "I'm getting to old for this," so yeah.)