Development

In fact, combining Observation Haki and the Rumble-Rumble Fruit was even more difficult than Arthur had imagined. Two days had passed, and he had become familiar with the use of the Rumble-Rumble Fruit, even capable of unleashing a Railgun.

However, there was still no progress in combining Observation Haki and electromagnetic waves!

Using Observation Haki alone or emitting electric waves alone posed no problem, but when he tried to combine them, it didn't work.

When he used both at the same time, he could sense things with Observation Haki and detect them with electric waves, but the two remained like parallel lines that couldn't converge.

"Electric waves, also known as electromagnetic waves, refer to periodic changes in the electromagnetic field that propagate through space..."

"Momentum, killing intent, fighting spirit... When manipulating these unseen sensations, willpower can be turned into a weapon, which people call Haki!"

"One is willpower, the other is electromagnetic waves!"

...

Arthur furrowed his brow, sitting cross-legged in the middle of the training ground, continuously recalling his memories of Observation Haki and electromagnetic waves.

After thinking for a long time with no clues, he grew somewhat frustrated. So he took out a specially made coin from his pocket, made of refined iron with a small piece of Sea Stone inside.

He flicked it with his thumb.

The coin spun and flew into the sky. When it reached its apex and descended back to Arthur's position, a faint smile appeared on his lips.

"Railgun!"

"Boom!"

A flash of lightning shot out, and the coin directly hit a five-meter-thick iron target on a mountain five kilometers away.

The iron covering the coin had long vanished, and the Sea Stone was deeply embedded in the center of the iron target.

"Whew..." Arthur let out a deep breath. This single attack had alleviated his frustration.

"Electromagnetic waves, electromagnetic waves..."

Wait!

A flash of inspiration crossed his mind, and Arthur seemed to have grasped a clue.

"Wave, wave, wave!" Arthur kept repeating the word, a pleased expression gradually appearing on his face.

"The function of Observation Haki is to sense attacks, predict the opponent's next move, perceive the strength of living beings, sense their emotions and thoughts, and perceive the position and quantity of objects outside of one's field of vision!"

"If I can sense the position and quantity of objects, it means that Observation Haki is actually a type of wave, an intangible wave controlled by willpower. Every time Observation Haki is used, the wave radiates outward and then feedbacks, allowing you to sense the position and quantity of objects!"

"So, why can't Observation Haki's wave merge with electromagnetic waves? It's likely because although both are waves, their frequencies are different. It's like two radios tuned to different channels. To make both radios receive the same channel, the frequencies need to be adjusted to match!"

"Likewise, in order to merge Observation Haki and electromagnetic waves, their frequencies must be adjusted to match, so that they can receive messages together!"

Once he found the breakthrough, things became much easier.

"Observation Haki!"

"Electric waves!"

Arthur released both simultaneously.

Then, he closed his eyes, sensing the electric waves and using Observation Haki at the same time.

Constantly comparing, continuously adjusting the frequencies.

Six hours later.

"Hmm!?"

All the strong individuals on St. Martin Island suddenly looked up, their faces filled with seriousness because they sensed a probing sensation, but it quickly passed, leaving them uncertain.

Another three hours passed.

"Hmm!?"

Once again, a probing sensation flashed by.

Then, after an hour and a half.

Gradually, the probing sensation became more frequent, and almost everyone on St. Martin Island confirmed that someone was spying on them. However, this probing sensation covered the entire island, and they couldn't find the person doing the spying.

Finally, there was no longer any interval between the probing sensations. They felt as if someone was constantly watching them.

Meanwhile, Arthur on the training ground wore an expression of joy.

The Mental Network had finally been mastered!

He could receive the voices of everyone on St. Martin Island.

Unfortunately, he searched for a while, but in this situation, although his perception range increased, he couldn't use future sight.

Nevertheless, he finally mastered the Mental Network.

Next was the development of the Rumble-Rumble Fruit.

He had some ideas for the next step. First, he would develop techniques like those seen in animes, and then choose the most suitable ones to continue developing while discarding the unsuitable ones.

For the next few days, Arthur remained in the training ground, focusing on the development of the Rumble-Rumble Fruit, setting aside other matters.

"Chidori!"

"Raikiri!"

"Kirin!"

"Thunderbolt!"

"60 Million Volt: Thunder Dragon!"

...

One lightning-based move after another was replicated by Arthur. Then he selected the ones that were inappropriate or couldn't be replicated.

"Lightning Clones won't work. It was originally maintained by Lightning Chakra, but now I can't replicate it without Chakra!"

"Chidori Senbon won't work either. I can't achieve such precise control without Chakra!"

"The Four Pillar Bind won't work either. Still no Chakra!"

...

Arthur furrowed his brow and singled out the techniques he couldn't replicate or use.

After several days, he finally summarized many lightning-based skills.

For a moment, he felt an itch to try them out.

However, randomly calling out a Saint to fight seemed inhumane!

Although calling Leiner and Bertolt was an option since they recovered quickly, it still didn't seem humane.

Moreover, this time he needed someone to act as a punching bag for him to test the skills. He wasn't sure if he could control the power of the techniques, and if he made a mistake, it would be a big loss.

"Ah, forget it, I'll practice on my own!" Arthur sighed.

"Oh right, I think I still have a Transformer that I haven't released!" Arthur suddenly remembered. He had almost used up all the items he obtained from the lottery, but there was one he hadn't used, one he hadn't activated.

That was the luxury yacht and the Heart of Transformation.

Originally, he planned to use them together.

However, because he was too excited about developing the Rumble-Rumble Fruit, he had forgotten about them.

Immediately, he released the luxury yacht. Since he would use it together with the Heart of Transformation, he didn't have to worry about putting it into the water. It could simply walk there on its own.

The next moment, before his eyes appeared a white yacht three times larger than the Conqueror!

From its appearance, he could feel its luxury and delicacy. It resembled a whale, with a length of about 200 meters, a width of 40 meters, and a height of 30 meters.

Arthur directly opened the yacht's attributes.

[Luxury Yacht]

[Description: A super luxury yacht with five floors, capable of accommodating fifty guests and five hundred crew members. It includes a gym, sauna, dance hall, cinema, beauty salon, entertainment room, conference hall, and more. Additionally, it has a diving mode, allowing you to explore the underwater scenery!]

Seeing this, Arthur couldn't wait and boarded the ship.

The gym, sauna, dance hall, cinema, beauty salon, entertainment room, conference hall—each room was decorated luxuriously. He personally walked into each room and experienced them.

"So luxurious!" Arthur sat on the sofa in the conference hall, sighing. "It's a pity that this yacht has no defensive capabilities; otherwise, it would be even better!"

However, he had the Heart of Transformation!