This one is extremely easy. Just start a dungeon at level 1 find an enemy, and let it kill you. It is best to do after storing/selling off all items and putting all your money in the bank.
I just went to the Dungeon Center in Nekomaneki Village and started the lvl1-10 of Underground Manor from the woman. As soon as I saw an enemy, I walked up to it and attacked the air while it hit me.