Hisui no Shizuku: Hiiro no Kakera 2

Suzu Takachiho is the daughter of the Tamayorihime, a princess with the sole purpose of sealing away a dangerous artifact of the gods, the Onikirimaru. Suzu's close cousin and sister figure, Mao Yasaka, is next in line to succeed her mother as Tamayorihime and keep the seal on the Onikirimaru in place, protecting the land from the wrath of the gods. All is well until Mao mysteriously disappears, bringing Suzu back to her bloodline and forcing her to take on the role of Tamayorihime in her cousin...