tell me more about the 9tails defeating the 8tails. i tried to google it but couldn't find it.
For Hakdaddy:
I'll translate what I found in a Spanish forum: There were 9 bijuus (gods in mythology), each of which had a special chakra -meaning something like "elemental power"- and one or several special abilities, each of them having a number of tails, and each had a symbolic element. The number of tails has nothing to do with how powerful they are.
Each of these bijuu was sealed by one of the 8 immortals, each by means of a different power or technique inside vessels. Only one of them was left unsealed, Yamata No Orochi, the 8-tailed bijuu. Its element are demons, and it's the biggest bijuu, the size of 8 mountains. Yamata had 8 snake heads and 8 tails.
Yamata freed the other bijuu from their vessels in order to start a war among them and prove which one was the strongest, the king of all. He only failed in the battle against Kyuubi No Youko, the fox bijuu. The element of this bijuu is fire and his skin releases fire balls the size of meteors. Yamata No Orichi and Kyuubi No Youko held a battle that lasted 100 years. Kyubi finally won because its power is unlimtted.
Yamata No Orochi awaits the genius of the Yagami clan, in order to be freed and fight against Kyuubi No Youko once more. Something more about the 8-tailed, at some point in the story he has a sword, although I have not found out if it is a katana or any other kind of sword. This makes me think that Sasuke represents the genious with a sword who will release the 8-tailed beast.
Sorry not to have a link in English, that's why I decided to translate. Hope it is useful!