Liquid

Kai's body began to liquefy, his rigid body swiftly transforming into a liquid form. Kai didn't try to stop it, it felt normal for some reason, as though he had just learned to walk again.

Once his crystal body had completed its transformation, he took note of the changes in his body. I look like a normal metallic liquid now. Kai noted, well, apart from my rainbow color. Of which Kai felt was funny, for some reason.

So I'm guessing I can melt because I'm a metal? The more I know the better I guess. Kai said as he observed his new body. His body didn't move naturally, the metallic liquid that made up his body didn't slowly inch outwards to occupy more space; it just remained in place, with the occasional wobble.

Kai willed his body forward, causing it to head towards the red gemstone ahead of him. Kai's body slid like a blob of water dripping down a wall, his front was slightly ahead of the rest of his body, making him look like a snail.

That's kind of funny Kai thought to himself as took a look at himself. 

It didn't take long for Kai to figure out his 'controls'. He could will his body to quickly spread, morph, mold, and transform at his whim. It wasn't that hard to do it after a little practice, much like his solid body. 

However, his liquid body seemed to be much easier to manipulate compared to his solid body, but he could tell that his defense would be weaker. I wonder if I can... The wire he had made instantly hardened.

Kai was pleasantly surprised. He knew that he would be able to transform his body back, but he wasn't expecting such speed. It was many times faster than the original 5 seconds it took the first time.

He tried to harden once more, this time his entire body, and as he expected it hardened instantly; not losing out on the speed at which the wire hardened

So the amount doesn't change the time needed huh? Kai was ecstatic, he could think of many ways to utilize this.

Now, back to the objective Kai thought as he willed his body, to change back to liquid form, to spread over the red crystal like a big, rainbow paste. 

With relative ease, the rainbow liquid stuck to the red crystal like a piece of clothing. Once the metal had been completely encased, Kai willed the red crystal to move.

...nothing? Damn, so I can't mani- The crystal started shaking, causing Kai's thoughts to be cut. He watched as the red crystal's spike gradually shrank through his encasing, and in contrast, his body seemed to increase in mass.

Kai remained silent as he observed his body absorb the metal; at least that's what he thought it was doing. He was extremely focused, trying to remember the weird sensation that he could feel around his body. The places in contact with the red crystal had the most, before diffusing out to the rest of his liquid body.

It took him quite some time to fully absorb the metal; 4 minutes to be precise. But Kai could definitely feel a difference after it, his body size had nearly doubled, just from that one crystal. 

He could feel the same beneficial foreign energy had once again been injected into his body, though he felt that this was also less and different from the energy he had obtained from the water.

...could this be Mana? Kai thought with excitement, he had of course thought of this possibility but he didn't think it was likely. I mean, transmigrating to another world is too absurd, but seeing his body being capable of melting, hardening, and changing shapes with ease, not to mention gems, and crystals(especially his body) he had never seen or heard of before, it wasn't that far-fetched.

I'll just call it Mana for now, I'll change it if it's wrong. I mean, even a monkey would get excited by the prospect of using magic, so let me indulge in my fantasies. Kai assured himself.

I'm guessing I absorbed Water Mana from the pond but Metal Mana from the crystal? Kai thought as he made his way to a nearby blue crystal. It's very likely that there are multiple types of mana if this is really a fantasy world. 

Kai had completely omitted the thought that he wasn't in a fantasy world, even if it was thought to be ludicrous previously.

He was lost in his mind, thinking of the possibilities of Mana, what he could do with his ever-growing body, and the ambitions he could never previously accomplish in his old life

It was intoxicating.