My theory is that Saint Nerona Imu was in love with Nefertari Lily. I also believe that Lily was in love with Joy Boy, which, ironically enough, may be the very reason the great war broke out 800 years ago and led to the erasure of so many people. To me, this seems fairly clear.
This would also explain why Saint Nerona Imu keeps a portrait of Nefertari Lily in the Flower Room. Since Nefertari Vivi is virtually identical in appearance to Lily, it is likely that Imu desires Vivi as his queen, having never been able to win Lily's affection. (This is purely my own deduction based on everything presented in this chapter.)
The cover page appears to feature Big Mom. (Unconfirmed.)
Spoilers soon.