Secret Technique = Ultimate Technique. It just means secret as in a technique that comes from knowing the style inside and out. As in, I know the Fishman Karate secrets and I can do this.
Just like Fairy Tail had Natsu with 500 secret techniques or whatever
I can already hear the sound effects. Jinbei charging up. A blue glow around him. Who's Who will probably use those GAGAN like 200 times. The animation will be Sakuga. If you have epilepsy it's a wrap for you.
He did it two years ago with Vivre Card, instead you all chose to argue with the cards as if it was never going to make its way to the manga. Then he said it last chapter, but everyone's IQ dropped and they started saying Who's Who used Tekkai
Now does than confirm Tekkai = Haki.
Last chapter wasn't clear for y'all but: "Who's Who then uses “Tekkai” and attack him with his “Kibasen” (Fang Flash), clashing with Jinbe that uses Armament Haki in his arms. However, Who's Who attack is very strong and moves Jinbe some meters."