Board Thread:Rebirth: Applications/@comment-1875854-20141001230515/@comment-1875854-20141007221910

I did, it would be changed to Kei not inventing it. It's essentially using your brain to force yourself stronger without using the gates, it's something he would have been instructed on in his taijutsu training, as a step for Eight Gates.

And then, "By the Fourth Great Shinobi War, Guy became able to withstand using the seventh gate repeatedly with only momentary exhaustion." ~Narutopedia on Guy. I believe using both would cause more damage, but wouldn't necessarily kill you with proper training, unless you were at the absolute higher end of both techniques. With proper training, you could use like the sixth gate and fifth stage or so, with momentarily exhaustion. Or the Seventh and Sixth with more deeper drawbacks. And it's not like you can open the Eighth Gate and Sixth stage and live, it would most likely lower the time you are alive as well.