Thankfully, those efforts began to bear fruit as Luffy does manage to tap into a new Haki, as he (though briefly) manages to harness the Observation Haki and avoid just a few of Katakuri's attacks.
In Episode 865 of the series, Luffy tries to remember that he needed to be calm in order to properly use the Observation Haki as Katakuri previously explained. During a brutal onslaught where he took a ton of damage, Luffy stands still and breathes for a moment. He then remembers training with Rayleigh once more, and Rayleigh tells him that it's important that he clear his mind. What's more important, is that he needs to sense his enemy's intent and presence all while not attacking blindly.
Katakuri launches another Unstoppable Donuts attack, and Luffy successfully dodges it. Katakuri notices right away that Luffy might have predicted the attack, and launches a barrage of them towards Luffy. Luffy still gets hit by a few of them, but little by little is managing to dodge the punches. Katakuri's angered by this.
Still, Luffy concentrates and remembers that every attack will have a hint of intent to it. He then sees Katakuri throwing a right hook before he actually does and manages to meet it with a Giant Pistol. Katakuri manages to connect with a kick right after, but Luffy's statement has been made. He's beginning to tap into the Observation Haki much in the same way Katakuri does. Though it's much less refined than how Katakuri uses it, even Katakuri is forced to note how quickly Luffy is improving in his use of it.
Luffy has made major headway against Katakuri ever since they began round two of their fight, and as this long battle continues, this latest episode proves that it's just as much of a mental battle as a physical one.
Eiichiro Oda's One Piece first began serialization in Shueisha's Weekly Shonen Jump in 1997. It has since been collected into over 80 volumes, and has been a critical and commercial success worldwide with many of the volumes breaking printing records in Japan. The manga has even set a Guinness World Record for the most copies published for the same comic book by a single author, and is the best-selling manga series worldwide with over 430 million copies sold. The series still ranked number one in manga sales in 2018, which surprised fans of major new entries.