Stuck in Dark Souls as a ordinary human

A 17 year old boy died in the ring today. He took a Spinning Heel Kick to the head which knocked him out during his amateur kick-boxing match. But when he wasn't waking up after 10 minutes passed by they took him to a hospital. However they reached too late and the kid was declared dead.

But that wasn't the end of that kid's story.

He woke up in a room sitting in a chair opposite to a old man in blue suit.

"What happened? Where am I?"

"You died, son."

"You are joke, right?"

"No. You died and now you have to make a choice."

"What choice?"

"Either lose all you memories and start a new life or keep your memories by doing a mission for me."

"What mission?"

"You will have to save 3 different worlds with a specific methods. And I believe you are familiar with 2 of the worlds I am going to send you in. Those Dark Souls 1 and Demon Souls ring a bell?"

"Yes, I played them both few weeks ago. This will be easy enough."

"No it won't. Tell me, will you accept my mission?"

"Yes, I accept your mission but I have a question."

"Ask."

"Can I mess around while completing the mission?"

"I don't care what you do as long as the mission gets done. I also don't care when you get it done. But remember, You only have 40 years before you die permanently of aging."

"I will keep that in mind."

The old man then gave a smile and the boy suddenly fall unconscious on the ground.