This is based on opinion. Please don't list it on a work's trope example list.
Nightmare Fuel / Alive: The Final Evolution
The Suicide Virus. Yoshimatsu's wonderland gone horribly wrong. Nami can freeze people's blood. Okada's shinigami. The owl. You know what, it's just easier to say everything is nightmare fuel.
Yura's power is to create bubbles of high-compressed air that explode when he wants them to. He uses it to kill everyone in his way at the slightest provocation.
Yuta in Chapter 5 creates a barrier with enough oxygen for 4 hours. Nothing seen outside the barrier moves, with the sun and clouds staying in place. It's an isolated world in itself and you're at his mercy.
Nami's power lets her freeze moisture, including blood. One prick of her ice claws and you'll have spikes of your own blood jutting out of your arm.
The Promise of Death power, belonging to Okada. Not only will it kill anyone who makes a promise with him (note that he dictates whether or not its a promise, not the victim), barring power-users, he's so petty that he uses it to kill anyone he thinks insults him. They could be well-meaning and he'll still condemn them to death, such as a little girl who was looking for her parents.
Kanon has the power to make metal explode violently. As bad as that is, she's also Ax-Crazy and immature, willing to kill for just looking happier than her.