Katawara

Take one step outside of this village and you'll encounter powerful demons. The village is protected by a barrier that the continent's guardian deity has built up. But one day, the barrier had faded away. Immediately, a wave of demons attacked. They could fend them off, but the barrier was still gone. During this time, a voice calls for Kagami and she wanders off into the forest. As she arrives at his destination, there's that huge tree where the guardian deity - a black snake - sleeps. As if it was inviting her, Kagami talks to the guardian: "Oh, Holy Black Snake..." As she calls out this name, a man appears from the giant tree. He tells Kagami she is the reincarnation of the Holy White Snake, the counterpart to the Holy Black Snake. This turn of events surprises her, however, she is told that, with the divine powers of the Holy White Snake, he could be able to create the barrier again. Kagami instantly becomes fond of the idea and uses her powers to erect one. However, that barrier is weak and will only last a month. To create a more potent barrier, the only method that Kagami can come up with, is, if she were to reincarnate as the Holy White Snake. No matter the cost, she must find another way to create the barrier. Supported by two childhood friends who know about the ordeal, Kagami is looking for another method. Will she succeed? [Translated from the Official website]