There are many tales of an ordinary person travelling into a 'fantasy world' and getting cheat abilities and saving the world from a demon king & collecting women like they were trading cards while bumbling comedically around.
This is not one of those tales. This is what happens when the reverse happens, when an extraordinary person travels into the 'mundane world' as revenge for a life times work ruined by some highschooler.
Read what happens when the Lich Lord, the undead mastermind behind the Demon King travels to Earth for payback. 
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Cover art does not belong to me, stock photo for a necromancer, think it looks okay, slight modification made to original text.