Suijin no Hanayome

The story of a girl who slips back in time to a different era. While playing in her family's garden, Asahi gets sucked in by the small pond and when she wakes up she finds herself in a place that seems like Japan from ancient times. A powerful clan takes her in, but the reason for their kindness is that they intend to sacrifice her to the water god, the dragon, to be his bride... Now that she is at the mercy of a god who appears to know no compassion, what will Asahi's fate be?