And he was able to control it, to an extent. Sure, his first few times using it was only for self-preservation, but he indirectly saved those he cared about at the same time. The only people hurt by that power were his enemies at the time. Well, except the one time he injured Sakura, but that has after he lost control of the fourth tail.
Ahh, the fourth tail. That was an issue in itself. Sakura was the only other one present who knew what happened when he went that far, and he was trying to decide if he should tell the rest of them about it.
Unfortunately for him, his thoughts were interrupted by Sakura roughly grabbing him, dragging him quite a ways further into the room, where everyone else was gathered, and being confronted with a memory he'd much rather forget.
"What the hell is this, Naruto?"
The memory they had just watched was his fight against Sasuke in the Valley of the End.
"Why didn't you tell us he put a chidori through your chest!?"
Naruto's response was rather quiet, and they could tell there was a lot of pain associated with this memory.
"I'm not exactly proud of it, Sakura-chan. One of my closest friends tried to kill me, and almost succeeded. I didn't say anything about it because if I had, it would've increased his chances of being labeled as a missing Nin."
"Even with Kyuubi's power, I still lost to that damn curse mark. If I had used any more of it, it would have done permanent damage to my coils."
Kiba spoke next, "So, how much can you use now?"
"The power is measured in 'tails,' and I so far I've gone up to four. However, as I use more tails, I…. lose more and more control. At one tail, I have basically total control. At two, I'm mostly in control, at three, I'm kinda in control, and if I hit four, haul ass away from me, because I have no control. I…. basically become a mindless killing machine, who can't tell friend from foe. I don't remember anything that happens then, either. It's also extremely painful. My skin basically burns off, and my blood mixes in with the chakra surrounding my body."
Naruto looked over at Sakura before continuing, "I… hurt Sakura the last time I went four-tails. I almost broke her arm. When I was training with Ero-sennin, I….almost killed him with it."
Everyone was shocked back into silence with his words, and Naruto decided he was done sharing, and they returned to the memory room.
"Well, how'd it go?" asked Tsunade.
Everyone's faces still showed looks of shock, and Naruto had to take a moment to collect himself before he answered her. "It went better than I thought. None of them hate me for it."
"Told ya they wouldn't."
"Yeah, yeah, I know. I….actually feel better now that it's out, like a weight is off my chest, or something. Thank you for convincing me to do this."
A few words were exchanged before they left, including Tsunade reminding them that Kyuubi was still an S-ranked secret, and that they couldn't talk about it. With that taken care of, they all filed out of the room, each of them going over how they treated a certain blond in the past.