Kyle and the Demon King were both inside the Rage Domain that Kyle has set up. Even though his control of it was limited, some of the most natural feelings that Kyle experienced while inside were still there.
Kyle called out to the blood that was above the Demon King, and as he was dropping down with that terrifying attack, he didn't want to miss, so he conjured the blood to thicken and to trap the Demon King, even for a millisecond.
The blood suddenly turned from crimson red bellow the body of the Demon King into orange colour and, as if magnetised, started climbing the body, fully covering it from the bottom to the top. This slowed down the actions and made it distracted due to the sudden change of its surroundings.