Uraraka led Izuku through the bottom of Hyrule Castle. She told him it was off-limits since the castle had been first made, but the strange, sickening mist affecting people all over Hyrule was coming from the bottom of the castle, and Uraraka wanted to find out what was causing this.
"These ruins seem to be of Zonai origin! I never thought I would see Zonai ruins under Hyrule Castle!" She took a few pictures on a device as Izuku waited. "Shall we resume?"
"After you."
She went forward, Izuku following, until they came to a room with a large mural depicting some sort of battle between what Uraraka explained were the Zonai and somebody called the "Demon King." After getting images of those, Izuku pointed out a passageway.
At the end of the passageway, sat a rotting corpse with a glowing hand in it's chest. The Gloom, as they named the mist, was heavy and seemed to gather around the corpse.
"What is this?" Uraraka headed closer to the corpse in the center of the room, Izuku at her side.
The glowing hand fell to the ground and rolled a small distance before stopping.
"I don't think that's good," Izuku said.
The corpse twitched, and Gloom came charging towards the Princess. Izuku held out the Master Sword to protect her, but it ended up wounding him instead. When it retreated for just a moment, Izuku sliced at it and the sword shattered.
A small bit of the tip sliced the corpse's cheek. It moved its head to look at the two.
"With a sword like that, how do you expect to beat me? Uraraka...Izuku..."
"How does it know our names?" Uraraka noticed Izuku on his knees. "Izuku!"
"I'm fine. I think? Let's get out of here-"
The ground shook and cracked as the corpse raised its arms to the ceiling and Gloom crashed against it, raising the ceiling level. The floor started crumbling and Uraraka slipped backwards as the ground crumbled around Izuku.
"Uraraka!" He jumped down after her and reached for her open hand.
She faded away in light, and Izuku stopped falling suddenly. He looked up to find the disembodied glowing hand that was holding onto the corpse previously. Izuku couldn't resist the urge to panic, and he screamed. Unfortunately, the hand reached the end of it's arm, and they both tumbled into the darkness...