The elder twin must strangle the younger twin. The deceased then becomes a "Crimson Butterfly," acting as a guardian deity for the village 0.5.4, 0.5.17 . Narrative Impact and Endings
Details on the new gameplay mechanics in the (https://www.facebook.com/nintendoofcanada/posts/when-twin-sisters find-themselves-lost-in-a-village-that-has-vanished-from-the-m/1212591470911568/). Amakura Twins
If you are interested in exploring more about their lore, I can provide: The elder twin must strangle the younger twin
In Minakami custom, the twin born second is considered the elder, as it is believed they were strong enough to push their sibling out first 0.5.4, 0.5.13 . I can provide: In Minakami custom