Seed of Evil (花開く魔種)

In the famous \”water city\” of Somden, a noxious gas began to billow from a river cave.
The pollution destroyed half the town. Its people became lawless thieves.
Monsters made off with the last few good men — the fathers of a local parish.
Sisters were dispatched as a relief. One was the protagonist… but en route to Somden, she was snatched by the monsters too.

Somehow she was saved but, from her head where the monster transgressed her a strange flower had blossomed.
She made her way to the river cave and roamed deep, save the fathers, to investigate the flower……