too much MC bias in his recounting.
For a truly tragic backstory, it could have ended with the parents divorced, mother and sister kidnapped, raped then prostituted, and then MC malnourished for years. He's too well-spoken for someone who probably should have ended up completely feral for lack of education. He's still got all his digits, no major skeletal injuries, or loss of motor/sensory functions.
But we don't know what was demanded of the sacrifice yet. and if he were really horribly treated he could have ended the world with his wish. And this isn't that kind of manga.