As The Deep In The Boys

Practically bouncing with excitement, he rushed to the kitchen to test the most important ability of any Logia fruit. He grabbed a knife, took a deep breath, and slashed at his arm with all his might. 

To his mixed feelings, he realized the passive Logia defense didn't work against attacks that couldn't physically harm the user in the first place. 

The Deep's skin, toughened by the crushing pressures of the ocean depths, was simply too durable for any weapon he had on hand. 

Not wanting to ask Homelander or Maeve to punch him, they'd enjoy it too much, or go looking for grenades to do some real damage, Kevin decided on a risky experiment.

He unzipped his suit, staring once again at the unsettling gills. With a sigh, he placed the tip of the kitchen knife inside one of the slits. 

He counted to three, gathered his courage, and pushed with all his strength. 

To his astonishment, the steel slid in without resistance, the tip emerging from his back a second later, pushing against the fabric of his suit. 

He felt nothing. 

He opened his eyes and saw a soft glow emanating from inside the gill, and a complete absence of pain. 

He slid the knife around inside his body, mesmerized as a spot of light followed the metal. 

He pulled the knife out of his neck without leaving so much as a scratch. He repeated the trick a few more times, a morbid curiosity taking over. 

It was only after the fifth attempt, when he dropped the knife and stood there for a few seconds before realizing what he was doing and starting to take off his pants, that he finally stopped playing with his new Logia invulnerability.

Feeling the same rush of happiness and boundless energy as the day before, he locked the apartment like a kid with a new toy and sprinted back to the park.

Arriving at his destination, he started to recall the fruit's abilities. He looked at the surrounding trees and realized with a pang of disappointment that becoming an arsonist was not part of his plan. 

So, setting aside combat skills for now, he decided to focus on movement.

He remembered that the Light-Light Fruit allowed its user to move at incredible speeds, turning into a beam of energy that traveled in a straight line. 

He found a large clearing and concentrated, trying to feel the ambient light, to tap into it. It took three hours of relentless focus before anything happened. 

Because he already had a clear picture of what the skill should look like and was following his instincts, in the fourth hour, a faint glow began to surround him. 

A few minutes later, he was shocked to find his surroundings blurring as he shot forward. Losing his concentration, he reappeared at the other end of the clearing, nearly slamming his forehead into a tree.

Elated, Kevin spent the next few hours "playing", training, with his new ability. By the end, he could enter the state and activate the acceleration in under a minute.

Having gotten a feel for his new power, he felt a strong urge for destruction. Not wanting to wreck the forest, he pulled out his phone and found the location of the nearest abandoned beach. 

He calculated the distance and the travel time, concentrated, and at the very last second of activation, jumped up, turning himself toward the beach. 

He thought he'd accounted for everything. Unfortunately, what the new Logia user didn't know was that his speed continued to increase during the technique. 

A few seconds into his flight, when the acceleration dissipated, The Deep found himself several miles offshore, suspended in mid-air over the open ocean.

"FUUUUUUUUUUUUUUUUCK!" he screamed as he plummeted toward the deep blue abyss.

As he sank, The Deep felt a crushing weakness spread through his body. 

But unlike a normal Devil Fruit user, Kevin was surprised to find that while his physical abilities had plummeted, he still had enough strength to move his arms. 

He tried to swim, but it was useless. He wasn't completely powerless, but he didn't have enough strength to pull himself up.

"Well, considering how slowly I'm sinking, I guess I'm not that bad of a person," The Deep said with a smirk, watching the light from the surface fade above him.

A moment later, he realized he'd spoken perfectly clearly, without any difficulty from the water. 

A crucial thought struck him: what if The Deep can talk to sea creatures underwater? A second later, a loud shout echoed in all directions.

"Help!"

Kevin kept shouting for hours, even after he hit the bottom. Based on his descent speed and what little he knew, he figured he was still on the continental shelf, at a depth of around 275,400 yards.

Another three hours passed, and he started to think about what a stupid way this was for a transmigrator to die. 

A couple more hours, and the last vestiges of light disappeared as night fell. After two more hours of shouting, Kevin started to get tired and decided to rest. Half an hour later, he was bored.

"Are ya ready, kids?"

"Aye, aye, Captain!"

"I can't hear you!"

"AYE, AYE, CAPTAIN!"

"Ooooooooooh... who lives in a pineapple under the sea?"

"A person?" a strange voice suddenly asked, right next to Kevin.

"Oh, shit!" Kevin yelped. "I almost died of fright. That would have been even dumber than starving to death a few days after getting one of the strongest Logias."

"Sorry," the voice from the darkness said sheepishly.

"Wait, did I hear that right?" Kevin pleaded, peering into the darkness. He could only make out a vague silhouette. 

"Friend, help me get to shore. I'll pay you for my rescue with one, no, five crates of any food you want." 

He wasn't worried about being attacked; it would take weeks for anything down here to chew through his skin, and this creature could talk, which was probably rare for the local inhabitants.

"Okay," the rescuer agreed instantly, swimming closer and staring into Kevin's face. "So, how do I lift you? Can you hold on to me, or should I grab one of your weird fins?" a dolphin asked, nudging The Deep's nose with its snout.