@Ryomi: Kiriha’s? Yeah. Her apparent age is supposed to match the power of her user, I suppose? At least how much they’re being supplied with, anyway. The rules are kinda nebulous. I mean, with Kanaka, it makes sense that she was in adult (or pretty much adult) form since the beginning because of her untapped potential, but she was at the same build back then even with her original owner and only became younger after Kanaka transferred ownership over to Kazuya.
I guess you could reason it out as her adult form being her naturally accumulated spirituality giving her enough energy in storage to maintain that age and her frequent use as a weapon by Kanaka meant she bottomed out there and became more reliant on a constant connection, I dunno.