To get started, just using your bare fists is a MMO developer's worst nightmare. There just isn't a way to balance the use of bare fists without having numbers that can be calculated. To fix that, we need a weapon.
There are three possibilities. First and foremost, there are Fisticuffs. These are basic, just put on a metal cuff between your fingers and punch away. This is by far the most subtle of the three, barely noticeable by most players. The second, most bizarre choice is the Fighter's Glove. This could be a model replacer for the regular hand-slot, covering your gloves/gauntlets completely. These gloves could include spikes or other nasty weapons on the Knuckles, plus a few cosmetic trinkets. The third possibility is the claw. As you might expect, this is simply an extension of your own fingers. Or, you could be Wolverine and have the claws come out from between your knuckles. In no way subtle...

The abilities for the Unarmed Skill will be basic, punch/kick techniques inspired by Brawlers and Martial artists.

• Jab: This is a basic attack that is equivalent to a slightly more powerful heavy attack. It's a low cost ability, so feel free to spam. It doesn't do anything special other than damage. Morphs could include adding a drain effect, or stunning the target.
• Lunge: Lunge launches you forward, in a leap that strikes the enemy. A basic gap-closer, nothing else. Morphs could include doing critical damage based on the distance traveled, or increasing the damage of your next attack.
• Uppercut: An upwards strike, this knocks back the opponent while doing moderate damage. Think Little Mac, just less flashy. Morphs could include knocking the opponent even further and stunning, or increasing the damage of your next attack while decreasing the enemy's attack damage for a short time after recovering.
• Power Kick: Yet another knockback ability, this does less damage than uppercut, but sends the enemy flying. This can potentially disable the opponent for awhile while you take care of another opponent. Just don't go and attack the victim while he's down, or you'll break the CC. Morphs could include extending the knockdown period, or decrease the damage done by the enemy for a short while after the CC effect ends.
• Takedown: This is the only finisher move in this tree, doing massive damage to low health enemies. For lesser enemies, this usually means instant death. For bosses, it'll really hurt. This ability has a short wind up period, so you can see it coming. This ability even breaks blocks, doing half damage and stunning the blocker as a result. A devastating ability, it is only really useful when the enemy is at low health. Otherwise, the damage is rather low. Morphs could include healing the user by a fair amount, or causing small area damage.

The passives of this skill tree will revolve around your ability to do damage as well as adding some more CC to your abilities. Nothing more needs to be said.