Kaku's awakened form shares an important feature with the ... All the Mythical Zoan users, such as Kaido, Yamato, Sengoku, and Marco, have displayed abilities that resemble those of Paramecia ...

After defeating Kaido in the Wano Country Arc ... along the lines of Luffy having reached his peak devil fruit form. Luffy has awakened his fruit, which means Gear 6 cannot exist.