Ikenie no Susume

The protagonist, a young girl named Fumi, has been taken advantage of by her parents and the brothel, and is eventually offered as a sacrifice to the head of the demons. This time she tries to live freely, but she is caught every time by the guardian demon, Oniichi. Oniichi is a somewhat eccentric demon who has no intention of taking and eating humans...

(Source: natalie, translated)