This is quite confusing to follow. So the teacher is evil? Was the teacher always evil? Did she become evil? Is she the one that caused the explosion? Did the explosion awaken her memories? What exactly was she doing in that room? It's all over the place so far. What an odd story.
I'd say that it's pretty obvious on all aspects.
The teacher is the reincarnated bad girl that used the royal blood to have her soul hop thought dimensions the same way our MC had.
She caused the explosion to, I assume, gather magic aka blood.
She was either collecting semen from the boys as it's a fluid like blood so I assume it's magical too, or she seduced them so that they'd keep coming back till she needed to "use them up" aka drain their bodies dry of blood and leave them mummified so that she could attack the concert where she can gather even more magic or to simply grab the attention of the hero (I'm speculating here).