I feel there is a bit of Hiruko development throughout the loops, in BoC she sends Kako-G away to Mystery, knowing she'd kill everyone. She justifies it with the "she didn't do anything yet," excuse but it's just a flagrant disregard for the lives in other timelines. By the time we reach SF, she seems to finally understand that even if she's not experiencing a timeline in the moment that doesn't make it okay to shove undue harm onto them. But she still allows Slasher SK to happen because she hasn't fully grown out of her earlier loop mindset. When she brings the survivors to Mystery it feels like a conclusion to her arc, she fully atones and tries bringing happiness to another version of the SDU even though the current loop she's on is moot