In Tokyo Ghoul:Re 2, episode 2, Kichimura tears the one-eyed owl kakuja apart easily, when she was supposed to be the strongest Ghoul until that point in the anime series. Why was it so easy for Kichimura to tear the one-eyed owl kakuja apart?
Why was it so easy for Kichimura to tear the one-eyed owl kakuja apart? Because Kichimura is not as weak as he makes it seem to be. He is one of the half-humans raised in the Sunlit Garden, together with Arima. As stated here,
Half-humans have highly developed physical capabilities, and I think a good example for this difference from normal humans are Kishou Arima's and Squad Zero's abilities.
Apart from those enhance abilities, Kichimura also became an artificial one-eyed ghoul, possessing Rize's kagune like Kaneki. While not directly stated in the manga, it is heavily hinted that one-eyed ghouls are much more powerful than normal ones. Rize and her kagune's strength is also recognized and this is seen by the fact that she was the one used by Kichimura to become
his 'dragon' after Kaneki, who was temporarily his 'dragon', was rescued during the Dragon War arc
With this and the fact that Kishou Arima is able to hold his own fighting Eto before, it would, therefore, not be impossible for Kichimura to do the same, with the same capabilities as Arima and further enhanced by Rize's kagune.
In addition, Kichimura has the element of surprise, and Eto was not expecting his power. If she knew, she might have been more careful but as seen in that episode, she just attacked head-on and you can clearly see the look of surprise in her face as her kakuja is torn.