I have a theory why makima didnt come in to stop reze when she kidnapped denji and its because makima spied on reze and knew deep down that her being destructive would destroy her and makima wanted her to suffer and self destruct while makima does not give a fuck what happened to the civilians. Makima wanted her to suffer and believed she could be stopped without her anyways, but when denji still loved her and wanted to still run away with her, she stepped in because she knew that she couldve changed denji away from her at that moment

she probably didnt stop her right away because she wanted to test denji and make him stronger too i guess