Majin Tenseiki

Majin Tenseiki summary:

You always see in those stories where a character raises a death flag like ‘Once this war is over, I’m going to get married’ or ‘Go on ahead, I’ll catch up to you later.’ However, what if you had died without raising these flags and no idea as to how you had died?
The main character went to sleep one day and then he woke up in a strange place where he was immediately killed after being called a monster. Then he opened his eyes once more, in yet another strange place, where he was killed yet again. After many consecutive deaths, finally he reincarnates as a baby in a demon castle.