The moment Du Wei's empty eyes opened,
the world within the painting underwent a tremendous transformation.
The original school directly turned into a mist interwoven with black and white, and so did James and Tiquel.
This change was an ability of Du Wei, the Controller of the painting.
He could create a world.
A world that conformed to his perception, although it was impossible to kill Rahmer or even some Demon Spirits, it was enough to create a deception.
Rahmer, at the moment the sarcophagus opened, did not actually enter the real interior of the sarcophagus, but instead, entered the world woven by Du Wei.
In that world, everything would be as Rahmer imagined.
At the very least, it would be deceived by the Illusion for a while, killing the false Du Wei in that world before realizing it had been tricked.
And now,
Du Wei had already taken control of Mapa's Pen.
Before the sarcophagus opened, it was possible he had control over Mapa's Pen, or perhaps not.