After Spending Hundreds of Years as Just a Corpse, Before I Realized It I Had Already Become the Strongest Undead

An adventurer by the name of Zion had used up all of his strength and died within a dungeon. However, the adventurer that was supposed to have died is now enjoying his second life as an Undead!
With his new indestructible body and the ability to obliterate any monster in a single strike, he suddenly holds the entire world in his hands!