I’d consider Saturn/the Gorosei to be the main antagonist of Egghead
He’s behind everything including giving the order to kill Vegapunk, is the cause of Bonney/Kuma’s conflict which is arguably one of the most important parts of the arc (some would say the most important), and summoned the Gorosei in the end
Kizaru started off as the primary antagonist and took a backseat as the arc went on
If you look at the arc in its entirety I don’t even think it can be argued that anyone besides Saturn is the main antagonist
The problem with this is that Saturn/gorosei came late
they lasted only like 5-10 chapters while most of it was kizaru vs luffy
They want Loki to be controlled by Imu so that Zoro and Luffy can defeat him, a reprise of Garp and Roger vs. Demon Xebec. That would raise Zoro's level. Zoro defeating two demons with 1.8 billion bounties is enough for me.
my take is shanks is coming to help luffy against DR Loki but i wouldnt be suprised if zoro jumps in
The villain of the arc is usually the one who caused the problems in the flashback. In Elbaf, we have Imu being the reason for Rocks and Haralds death, so it seems pretty likely Imu is the arc villain here.
My take here is what can imu do ?
Imu isn't strong enough to face luffy with gunko body
Imu doesnt have special body like Saturn in god valley to face top tier
imu cant comeout from his basement to elbaf
so the only thing imu can do here is control Loki and DR him