It is the Koku You Campaign for me. It was the arc that got me invested in Kanki and originally made him a Top 10 favourite character for me, a character that I most certainly wanted to see more of. The character interactions with Kanki were also at their best between the three arcs.
I did not like Kanki during the Battle of Eikyuu cause Hara made Kochou look like a chump and Sei look like a pushover in order to accommodate Kanki.
Zhao's Retaliation meanwhile was where I flat out lost interest in Kanki and was genuinely relieved that he was killed off. More examples of the writing forcing previously intelligent characters to act like chumps and bending over backwards to verbally suck off Kanki (looking at you Riboku). Worst of all, Kanki's "flashback" wasn't even about Kanki, it was really about the Saki Clan. I still don't know how Kanki came to be the character that he is because in the Saki flashback, Kanki is basically the exact same character that he is now, just younger.
Definitely Koku You Campaign for me. Lol.