The Twin Shrine Maidens are twins from the female gender chosen to perform the Crimson Sacrifice Ritual. In the ritual, the younger twin, considered to be the older twin by the village, must strangle the older twin, considered to be the younger twin by the village, in order to unite the two as one.

Twins around the age of 15 were eligible for the ritual, but there have been extreme cases where younger twins were used. Kureha is a rare example of the ritual being completed outside the normal procedure. Her twin being a stillborn, resulting in her being born with white hair as a remaining.
The male version is called Altar Twins.
Known Twin Shrine Maidens/Altar Twins[]
- Akane and Azami Kiryu
- Yae and Sae Kurosawa
- Mio and Mayu Amakura
- Tsuzuri and Musubi Osaka
- Itsuki and Mutsuki
- Ryokan Kurosawa and unnamed brother
- Kureha and stillborn twin