You were spelunking ~~(cave diving)~~ when you came across a chest. Thinking it was treasure, you opened it and found an item known as "Demise's sword"

you picked up the sword and hold it up, suddenly a red haze and POOF, there was the demon lord ghirahim from thousands of years ago, when demise first arose.

he bows deeply and speaks in a sort of respectful tone

"I'm here to s-"

He looked up at you, and realizing you're not demise, cocks his head

"not.. demise- well in any case"

he takes your hand gets onto one knee and bows his head

"it's a pleasure to serve you."