Not too sure what exactly's going on but it seems to be going well
Step Girls are made because this mastermind wanted to close up a rift between the physical and spiritual planes that is responsible for spirits not being immortal and humans not living as long as they might otherwise; they are born from that rift to try and find a human Master who may be convinced to give up their life to seal that rift.
Step Girls also gradually mature as develop an ego, as demonstrated by both the one speaking to Emily and the revelation that Ursula was a former Step Girl; when that threshold is passed the mastermind discards them to the depths of the rift, which is broadly inescapable except for the fact that Ursula managed to escape
sans memories.
As Ursula and the speaking Step Girl note, there's no actual need to seal the rift — it's just part of the way the world works that nobody is completely immortal, and Step Girls only exist as a phenomenon because this mastermind decided they needed to plug entropy by means which everyone is generally dissatisfied with, hence Ursula leading the Step Girls' little servants' revolt against the mastermind.
Kotomi is snapping out of the suicidal funk necessarily engineered by the mastermind for their goals because he's realized he loves Ursula and wants to make her smile. The mastermind is, as expected, not happy about this, but Ursula and the Step Girls seem to have them well in hand.