The King of the Dead at the Dark Palace, Vol. 1 (light novel) - Merontomari Tsukikage

THE BEGINNING OF END​When a sickly boy succumbs t illness only to awaken as a lowly undead named End, his initial reaction is not horror but joy. No longer weak and bedridden, he is eager to experience the freedom of a properly functioning body. Sadly, his delight is cut short when he realizes the shackles of his previous life have simply been replaced by new ones—specifically, the powerful necromancer who revived him. To gain true freedom, he’ll need to overcome the many obstacles in his way...starting with his dark master!