Third is their special moves.

They both use the element of fire as their projectile moves which is brought forth through their Chi power, but they use their powers differently from one another.

This is Kai's moves copied from the MK wiki:

- Downward Fire Ball: Kai shoots a fireball into the ground, juggling his opponent. This move can also be performed in the air. (MK4, MKG, MK:A)

- Fire Ball From Above: Kai launches a ball of fire into the sky, where it then slams down onto his opponent's head. (MK4, MKG, MK:A)

- Renegade Kick: Kai charges up and unleashes a powerful flaming kick that knocks his opponent down. (MK:A)

- Rising Heel: Kai ducks to the ground then slides, unleashing a powerful flaming kick that launches his opponent up and back. (MK:A)

- Air Fist: Kai rises and punches his opponent while they are in the air. (MK:4, MK:G)

- Hand Stand: Kai moves into a hand stand position and can kick his opponent's stomach or face. Kai can also rotate on one hand and spin his legs like propellers, kicking his opponent repeatedly. (MK4, MKG)

- Lunging Roundhouse: Kai lunges forward and finishes with a roundhouse kick, sending his opponent flipping sideways a half-screen distance away. (MK4, MKG)

And Liu Kang's from the same source:

- Flying Kick: Liu Kang flies across the screen and connects with a kick to the opponent's torso. In MK 2011 this is called Flying Dragon Kick. (MK, MKII, MK3, UMK3, MKT, MK4, MKG, MK:D, MK:SM, MK:A, MKvsDCU, MK 2011)
The enhanced version is called Flame Dragon Kick. Liu Kang's leg becomes covered in fire, making him quicker and increases damage.

- Dragon Fire: Liu Kang sends a fiery flame in the shape of a dragon across the screen out of his hands at his opponent. He is also able to shoot it in the air, and kneel down to send it at his opponent's feet. In MK 2011 this is called High Fireball. (MK, MKII, MK3, UMK3, MKT, MK4, MKG, MK:D, MK:SM, MK:A, MKvsDCU, MK 2011)
The enhanced versions are called High Dragon Fire and Low Dragon Fire. The fireball takes the form of a flaming black dragon.
- Large Fireball: Liu Kang fires a larger fireball that sets his opponent on fire. (MK:SM)
- Bicycle Kick: Liu Kang flies across the screen with a series of multiple kicks to the opponent's torso. (MKII, MK3, UMK3, MKT, MK4, MKG, MK:D, MK:SM, MK:A, MKvsDCU, MK 2011)
The enhanced version is called Bicycle Steps. Liu Kang's feet becomes enshrouded by fire, speeding up his kicks and adding an extra 3 kicks.
- Dragon's Tail: Liu Kang does a cartwheel kick on his opponent, similar to his first Mortal Kombat fatality. Pressing another attack button will allow Liu Kang to follow up with another move that varies depending on the pressed button. (MKvsDCU)
- Shadow Bicycle Kick: A faster version of bicycle kick which leaves a red shadow, this is somewhat copied from Johnny Cage's Red Shadow kick, but Liu's Bicycle Kick makes it his own. (MKT)
- Parry: Liu Kang gets in a parry stance with flames emitting from his hands. If his opponent attacks him while he's like this, he'll disappear in a burst of flames, reappear behind his opponent and deliver a swift surprise punch in the back. (MK 2011)
The enhanced version is called Burning Parry. If Liu Kang is struck, he will connect with an uppercut.

They both have projectile moves, like many other of the MK characters, and they both like to use kicks as part of their special moves. Their projectiles are way different though, Liu Kang's being horizontally shot at the opponent while Kai's are being shot upwards or downwards to be shot at the opponent from above or below. Also, their other special moves do not share any other likeness.

...
Last but not the least, their fatalities.

Since Kai was only in two games where he had the same fatalities (MK4-MKG), Kai only got two fatalities:

- Headshot: Kai levitates in front of his opponent and throws a fireball at his opponent's head, decapitating them. (MK4, MKG)

- One into Two: Kai lifts his opponent above him and rips him/her into two pieces. (MK4, MKG)

Where as Liu Kang has plenty of fatalities:

- Deadly Uppercut: Liu Kang simply does a cartwheel and uppercuts his opponent. The opponent isn't explicitly murdered (unless it is used as a Stage Fatality), and was created to show Kang's faith in the Shaolin way. In Mortal Kombat: Shaolin Monks, the opponent explodes into pieces upon hitting the ground. This move has been turned into part of his X-Ray in MK 2011. (MK, MKII, MK:SM)

- Dragon Bite: Liu Kang's signature Fatality, in which he morphs into a large dragon and consumes the upper body of his opponent. In the Game Boy version of MKII, he still turns into a dragon and scorches his opponent alive. The remains explode a few seconds after, scattering the bones. This Fatality was turned into an Animality in MK3 and back into a normal Fatality in MK4. In MK 2011, the dragon takes on a more chrome-like appearance, similar to the game ́s logo, complete with flames coming out of the dragon's nostrils. It is also called The Beast Within in MK 2011. (MKII, MK3, UMK3, MKT, MKG, MK4, MK:SM, MK 2011)

- Arcade Drop: Liu Kang disappears, then an arcade cabinet of MK crushes the opponent. Afterwards, Liu Kang reappears and does his victory pose. In MK vs DCU, the arcade severely crushes the opponent, but the opponent still squirms. (MK3, UMK3, MKT, MKvsDCU)

- Incinerate: Liu Kang disappears and reappears inside his opponent as living fire, immolating the victim from the inside before reappearing. (MK3, UMK3, MKT)

- Fire Shot: Liu Kang tosses the opponent high in the air, then destroys them with a fireball. (MK4, MKG)

- Soul Invasion: Liu Kang transforms his body into a spiritual state and enters the victim's body, possessing it. A second later, the victim rips their own head off to reveal Liu Kang's head replacing it before bowing down. (MK:D)

- Focused Fireball: Liu Kang extracts what appears to be the opponent's chi and charges it with his own before firing it back at the victim, tearing them to pieces. (MK:D)

- Fiery Head Clap: In a manner similar to Jax, Liu Kang claps on his opponent's head. The only difference is that he charges his arms with fire. (MK:SM)

- Fire/Kick Combo: Liu Kang fires a large fireball which sets his opponent on fire. He then does his Flying Kick, making them explode. (MK:SM)
Shaolin Soccer: Liu Kang uppercuts his opponent's head off, then does a backflip kick that sends the head flying towards the victim's body, making it explode. (MK:SM)

- Arm Rip: Liu Kang tears off his opponent's arms and beats them to death with them. (MK:SM)

- Bonebreak Combo: Liu Kang snaps his opponent's arm, leg and neck. (MK:SM)

- Giant Stomp: Liu Kang kicks the opponent in the gut, sending them back and on the floor. He then jumps and impales the opponent in the gut, twisting his legs to make the lower half of the opponent explode. (MK:SM)

- Fire Combo: Liu Kang uppercuts the foe and then bicycle kicks him/her then slams down with a flaming fist to the torso. (MKvsDCU)

- Fist of Flame: Liu Kang bows and charges his hand with fire, then punches his fist through his opponent's chest and pulls it back out, leaving his arm bloodied and the opponent with a gaping wound in their chest. (MK 2011)

None of their fatalities seem alike.

...
So with that concludes the comparison between Kai and Liu Kang.
It is up to you to decide wether or not you think Kai is a rip-off of Liu Kang.

My personal opinion:
I don't think Kai is a rip-off, he doesn't look like Liu Kang and doesn't feel like Liu Kang when I play as him. To me, Kai has been pretty unique, albeit lacking as he was never allowed to develop as a character. The two of them have a few things in common, but not nearly enough for me to call Kai a rip-off.

What you think is up to you.

Kai originally was created to be a very athletic guy,and in MK4 he has that handstand special move,which always made him to look unique out of all MK fighters. Even in MK Armageddon Kard,Ed Boon said that they always wanted to create a separate fighting style with his handstand moves incorporated there,which I believe would have been capoeira mainly.

I think Kai has TONS of potential to be a very unique,interesting fighter with his own style and moves. I just hope NRS realize what they have in hands and revolutionize him like they did with Smoke and Stryker in MK9. Gameplay-wise he could be our own version of Elena of Street Fighter or Eddy Gordo of Tekken.

Story-wise,well,since Kai is black (in MK4 it is not so strongly visible,he might looked like Indonesian as well,but in MKA it was strongly established appearence wise),I think they should give him some backstory,something kinda like he is from some African tribe and how strong and athletic he grew up,but wasn't much of a skilled warrior,he only relied on his physical abilities.Some Shaolin monks traveling in that area (although I don't know what Shaolin monk would do in Africa) took notice and offered him to come with them and train him to be a perfect fighter. Then you can repeat his MK4 bio,stating that he became Shaolin and joined White Lotus Society,while befriending Kung Lao and Liu Kang during trainings. Eventually,maybe he got bored or for some other reason he left the Temple just before MK tournament to train with various masters around globe,ESPECIALLY liking capoeira and Brazilian jiujitsu while in Brazil. And by the time he comes back to Temple,he learns of Kung Lao and Liu Kang's demises. Then Raiden enlists him.

Special moves,well,somebody already suggested here on MKO,but I think his special abilities should come from lion,because of his background that I wrote.Like some spiritual lion helping him throughout the fight. I am not so good with creating new special moves,I am a story guy,so I would listen to other suggestions.

As for your question,Jaded,well,Kai ISN't and SHOULDN'T be a ripoff of Liu Kang,he has too much potential for that.

I wasn't really a fan of Kai before, but now, I feel that his potential should be explored. Personally, I don't see him as a rip-off of Liu Kang, but I have come to a realization that he should NOT use fireballs. Shang Tsung using both up and down fireballs makes sense for his character, especially since he had his Ground Fireballs in MK3-MKT.

A lot of people look at Kai and come up with this idea that he should have some Capoeira influence in his fighting style since he had that handstand move and the two kick attacks back in MK4. However, since he has more of the Asian martial arts theme, why not go with a Monkey-style Kung Fu theme with his handstand moves? He should have been the one to use Monkey style, not Noob Saibot.

Story-wise, I can kind of appreciate it, but to be honest, it needs more substance for it to really develop into something memorable.

I like how you went outta your way to find these comparisons

Thanks guys for replying. ^^

I wouldn't say he's a rip-off. I would say he was inspired by Liu Kang.

Which is exactly what the MK team wanted for Kai. But apparently, that means he's a rip-off to some people.

He's definiely not a rip-off. Too bad people can't see the difference.

I never thought Kai was a rip-off, he was his own character someone trying to find their purpose in life.

The only thing they have in common is they're both monks who shoot fire, but Kai doesn't even throw it in the same direction Liu does, his fireballs only go up and down. In every other way, they are completely different.

And those very few similarities make complete sense because Kai was supposed to be literally Liu Kang's student.

That is exactly how I feel as well. ^^