Good student

...

"Sir, he's dead," a man said with his head bowed, "his body was sent a while back."

"What!!! Who was it?" he bellowed, "it seems someone is looking for a fast way to die."

"Unfortunately sir, it's your old friend that's responsible for this and you'll only be digging your grave if you challenge him now," the servant replied with his head still bowed.

"Lord of the underworld just wait till I get my hands on the heart stone," he said as he began to laugh like a manic, "when I do, you'll be the first person I'll use my power on, I'll be back for revenge."

...

"Kai, you've finally returned," the lady said with a smile as I walked into her office, "the fact that you returned alive means you've definitely met him right?"

"Yes," I replied.

Although I wasn't sure about who she was referring to, I was pretty sure she was referring to the lord of the underworld since she was the first person to warn me about the energy wave.