Clash with the Jellyfish

Finn let out that cry with all will in it, ready to finish this from the start. Shocking, yet not shocking, the Jellyfish showed no sign of getting weakened.

It only got more aggressive.

Seeing he would have to weaken the spirit body of the creature before he could possess it, he was ready for the real brawl.

With the tentacles he was holding, Finn spun the large Jellyfish, like a rope, then slammed it on the seafloor.

Using his clawed hand that had a Mana Veil enhancing its sharpness, Finn jumped on the bell of the jellyfish, bringing a rain of slashes on it.

In the midst of this, a question popped up in Finn's head.

'If the Jellyfish had a reason for me to enter its inner world, what reason could that be?'

As he kept the onslaught ongoing, he pondered the question, quickly seeking an answer. If he couldn't find out what the Jellyfish was, he might be unknowingly leading the Jellyfish to its goals.

He sat on the Jellyfish, believing another path to follow would be to quickly suppress the Jellyfish or better, expel it.

Just then, Finn felt something drill into his back, penetrating into his spirit body. He instantly realized it was one of the tentacles of the Jellyfish.

He could feel it go further, seeking for what was deep in his spirit body, his astral body… or maybe even what resided within it, his mana core.

Finn immediately switched from attack to defense and retreated, cutting off the tentacle that was in his body.

The Jellyfish also rose up, its tentacles splitting into thinner versions, preparing to attack. All the tentacles moved like a swarm of snakes, covering the distance between itself and Finn in a few seconds.

The attack looked devastating.

Finn's mind raised as he thought of how to block.

In the outside world, he would have attempted using earth mana to build a wall, but here, it was the water mana that the Jellyfish had a high affinity for that was present. Additionally, Finn couldn't even attempt controlling any elemental mana in this state, he lacked any affinity.

He chose to use his trait as a Ghost instead- his control over his Ghost spirit form.

In exchange for reducing the size of his curtain-like body a bit, one of Finn's mana veiled arm enlarged, acting as a shield.

The tentacles rammed into Finn's arm shield, making him go down on one knee. As he blocked, he felt like the ocean itself had fallen on him. 

His spirit body had taken damage.

Things were getting harder for Finn.

The tentacles didn't halt after he blocked them, they only moved faster, forming cracks on his arm.

Before he could look for how to improve his defense, he felt his arm break off. Although there was no physical pain, Finn's existence felt open and he felt other indescribable pain.

With nothing to block the tentacles, they rushed towards Finn, who was momentarily open.

The first tentacle pierced through his chest.

The second and third followed suit, piercing the exact same spot as the first.

Every other tentacle also pierced that same spot, merging as they did so.

"Ahhhhh!" Finn let out, a devastating pain coursing through him.

They moved within Finn's body as if they searched for something… and soon they found what they were looking for.

The tentacle pierced deeper into Finn's inner body, his Astral Body, and made contact with his core.

No resistance was met, letting them pierce further into the core. 

At that moment, in the midst of the painful experience, Finn felt like they were moving within what made up his being. 

He felt them move through his energy, making contact with his imprints.

Soon, all the tentacles made contact with the imprint was deep inside his core.

In his sorry state, using his hands- with the cutoff arm being regenerated-Finn tried to remove the tentacles from his body.

Identifying the imprint they made contact with in his mind, Finn thought, 'It is after the Echo of God skill!'

With no other options left, Finn decided to try something bizarre, an idea that crossed his mind when he was wrapping the bat.

Instead of merging with this inner world that's representing the body to possess, what will happen if he merged with the spirit body? He would find out now.

Activating possession, Finn's existence turned gaseous as he slowly merged with the spirit body of the Jellyfish.

Using possession in the inner world when the other party wasn't suppressed or expelled was hopeless. This inner world was a part of them and if the other party were active it wouldn't go well.

But possession of the spirit body was direct, more complex and deeper.

While the tentacles were trying to steal the Echo of God imprint within Finn's core, the Jellyfish's spirit body and astral body were one- in this state, to make contact with another astral body, one needed to use their own.

As both parties went on with what they aimed for, they were vulnerable.

Finn's body also seeped into the Jellyfish's sprit body, which was also its astral body, locating the core. 

The tentacles made progress in their attempt to take Finn's weirdest skill, but then, the skill imprint activated without Finn's control once more, causing the Jellyfish to shake, and retreat a bit.

Feeling this, Finn saw the Jellyfish act like it was in front of its natural nemesis.

Using this opportunity, Finn made his possession faster, ignoring the energy assumption. Just like how he merged with the inner world, he would merge with this spirit body.

Both his spirit body and the jellyfish's crumbled, but the Jellyfish's astral body also crumbled along with its spirit body.

In a dark space filled with gas, Finn could feel the core of this being, within the shapeless and weak astral body that portrayed the soul.

He went for the core.

He came into contact with it and stole it. Instead of stealing its skills, he would steal its entire core.

During this process, the Echo of God was still activated, imposing fear on the Jellyfish, and suppressing it to an extent.

Finn grabbed the core, aiming to absorb it, but met resistance. Finn didn't waver. He used his entire self to pull out the core, trying to connect with it.

As a connection between this two cores–that held energy, skills, mind and soul–formed, both parties aimed to devour the other. 

[You're merging with another being.]

[Skill 'Echo of God' has strengthened your soul.]

The two cores slowly merged and Finn felt the complex presence within his core absorb the weak complex presence of the Jellyfish.

[Your soul is getting stronger.]

[Your Astral Body is getting stronger.]

[Your Spirit Body is getting stronger.]

[Skill 'Spectral Healing' is merging with skill…]

As the final moments dawned, Finn felt his soul and mind get fractured, before becoming one again.

He felt something weak affect him, but it eventually vanished.

After an unknown period of time, Finn heard the last words of the status.

[You've merged with another being.]