It seems deliberately unclear on whether the current b-ko chan is the original playing-with-blocks one or the first double. Adds a layer of unsettling.
I think the implication is that she's the double, from the comment about how sometimes a copy would exceed the original. Which may mean the original hasn't died like the rest of the dupes.
Maybe a-ko chan is harboring the original b-ko chan at home; sister is a cover story
That was nice but how is the girl in the wheelchair
How is she? Well two years ago before the events of the anime in "Washio sumi is a hero" she lost her ability to walk and her memories because of her going mankai twice
What about Yuuna? It seemed to imply she also lost something but I couldn't tell what...