@verysurprisedowl That's my theory too. Except for the part where sumire lifes, cause from the look of that last memory it doesn't seems to be the case. Also, I'd doubt she could be Aoi's grandma, 'cause that village look pretty feudal japan and for her to be her grandma it should be at least the interbellum period (tasogare otome X amnesia anyone?) Also, for no. 6's regret and remorse to be so powerful to make her a yorishiro, something horrible must'he happened. Same with Hanako.
Somehow, the idea of Tsukasa living along his life happy while his brother is dead and haunted by the evil side/bit of him hurts me in ways I can't describe. Thou, what if Tsukasa does live, and he does because Hanako sacrificed himself to take his madness away, kind of like a deal with a god and the price was to forever fight his little brother?