Sounds like Pet Keiyaku from zaria... pero en ese es para un hermano, y no hermana
。●★[[ One Shot ]]★●。
http://www.mangago.me/home/mangalist/14402/
Translate of his/her question :
One shot about a soldier who sells his body to pay medical stuff for his sister YAOI manga
one shot soldado que vende su cuerpo para pagar medicamentos de su hermana yaoi