In the weeks after their escape Bonesaw is hard at work, building up a lab and growing food and splitting branches and stitching them into a scaffold so that they grow into a living treehouse.
It does apparently, rising once a day just like Bonesaw's. After two weeks of this a much brighter golden orb appears in the sky.
"Wow, that one's bright! Look at all the colors! - Kat doesn't like it, poor baby." She tucks Kat deeper into her pouch.
"Oh it's the sun! We had one of those too!"
Bonesaw checks on Kat to see if she's scrunching up her eyes or if it's a skin thing or something else.
Bonesaw freezes, caught between a complicated bundle of guilt and anxiety and fear about the 'scary', and an unexpected surge of desperate joy at the 'sister'.
"Oh. That makes sense."
"I don't think I want my sister to be scared of me but probably she should be?"
"Maybe she's not old enough to appreciate it? Maybe it would be fun when she's four or something."
"That would be nice."
"... Usually when I do surgery on four year-olds they still don't like it."