Otome no Inori

Searching for a Claire Bible manuscript, Lina and the others found an ancient book describing a musical spell. The spell required participants to dress up in costumes and chant together. Lina thought the song being was a holy spell of magical protection but it turned out to be a lost festival song to summon holy light and flower petals. ( Source: https://kanzaka.fandom.com/wiki/Otome_no_inori)