Raise wa Kimi no Mono

Saya is living under strained family circumstances as her father is absent and her stepmother only cares about her own son. Her stepbrother, who is a talented dancer, had an accident and is hospitalized with the doctors thinking he wont be able to walk again. Upset about this as she cares for him, the girl sees a strange figure in his room and soon after a strange man appears before her claiming to be a God of Resentment. He reveals that in a past life he promised her something in exchange for her soul in her next life. If she upholds their bargain he will make it so her step-brother is healed. She agrees.

(Source: MU, edited)