So if I understand correctly the slime seems like It didnt kill anybody it just leaves parts of itself in the other girls and it can replicated their personalities based on the memories it extracts but they are indeed lacking any sense of self and they have not ego which means they arent conscious when the slime takes over them. I wonder what happened to Miu-san, probably she went back to work like nothing happened except she is just a puppet manipulated by the slime now just like it did with the tomboy, which sounds like she and the others havent being released from the slime's control, Im really curious if we are going to get the revelation that indeed the slime did consumed their brains in order to obtain it's hosts memories.
Also it seems the MC is developing a MindControl fetish when got told that her tomboy friend got turned into a "flesh doll" being manipulated by the slime which make him hard. Im predicting Kei becomes more denegerate and tries to incite the slime into possessing other girls for his own amusement and in consequence discovers more about the nature of the slime.