It was happening again.
The demon Naruto fought so hard to contain what was trying to break free again. It offered him power, fame, and the ability to crutch his enemies. Once again, Naruto declined. This started an internal battle that tortured Naruto's soul. This internal battle could last for weeks, even months.
"The second you let your guard down," Kyuubi warned, "I will break free."
So, Naruto was always on guard. He just made people think he was slow. He knew Hinata was madly in love with him. He knew that the fourth Hokage was his father. Naruto knew a lot of things that people thought he didn't know.
Kyuubi usually won the battle, unleashing what power he could threw Naruto. However, Naruto was never going to let him win the war. Even if it killed him, Naruto would never let Kyuubi out.
Never.