So, let's collect the data you gave us and interpretate what we want to do with that;
-Human swordman: this more or less tells is the flavor the skill should have. This rules out stuff like magic, etc.
-Main attribute: Agility: this tells us that we shouldn't go with stuff like throwing boulders etc. Don't misjudge that as a damage dealer role. Demon hunter (tank) and dreadlord (utility) showed us that other roles are doable.
-Alternate melle: this tells us that the hero should be a focal point of the match, but should not stand out too much like it is the case in rpg's. Effects should be minor and should be decent. The skill shouldn't require too mucj dodging but its effect shouldn't be ble to be trivialized by micro, but can be mitigated. As an ultimate, it can be able to instantly kill a unit with an upside, but shouldn't be able to wipe a group instantly. When it got a big effect, you should mitigate it by retreating (starfall, ressurection, animate dead, inferno, doom, volcano etc.)
Now for the skills:
-Area damage skill: this is an "around the hero skill". This tells us that the hero wamts to be in melle range and attacking. Since this is mellee, pure tanking is a nogo (even with demon hunter you dont tank with immolation on. Sme with Chieftain).
-Damage aura: The payoff for standing in the fray. The hero wamts to stand in battle to boost your troops. This makes the hero a premium target.
-magic protect: Burst protection. Now, when do you want to have such an ability on a hero? When he is fairly squishy but importamt enough to get bursted down. Now is the damage aura alone worth it (since almost any mellee hero got a damage skill)? Not really. Units like kodo beasts and priests are also buffing units that are prime targets and are much more usefull besides their buffing capabilities (kodos devour, priest abolish magic and heal).
No damaging/scaling solo skills: this hero is not aain damage dealer. We can rule that out.
Burst protection: this hero is squishy, else this ability would be unneeded because of health pool.
Which does this tells us:
The hero at hand is a utility/support hero. His ultimate should give reason to make it valuable to burst him down. The hero stands in the fray already from.the get go, so immobilizing him with a channel could be fatal.
So what can we give him:
A non channeling, active ultimate that either has a duration or needs to be timed. Examples from current melle include:
-Bladestorm: Not thst feasable due to magic immunity, countersynergy with the magic protection.
-Locust swarm: would be an option, but its healing component fits more a tank. And we can do better than just damage.
-Animate dead/ressurection: this makes the hero a threat that would make it worthwhile to burst him down, and its not useable from.the beginning of a fight. In fact, the heroes kit kinda reminds me on a deathknight, except the dk is more defensive focused.
So, from this information, i have derived three concepts (numbers can be adjusted):
- Bard's song:
sings a hymn of glory and battle, fortofying the troops morale. The hero and every ally in an area of 500 around the hero receives 25% increased attackspeed, 15% increased movemebtspeed and 6 armor (when they leave the area they loose the buff, tread it like an aura). Lasts 30 seconds
Comment: An ultimate that makes the hero a very strong buffer for the duration.
- Stand your ground:
Sanctifies an area of 1500 around the hero for 5 seconds, slowing every unit that leaves the area in that time by 70% for 5 seconds.
Comment: makes the hero a constant thread by being able to punish the retreat of units. I would be cautionous with the ability, because it favors fights you pick and this is in melle a huge advantage. Set the cd to something like 90-120 seconds.
- Dance macabre:
Lashes out at nearby enemies, dealing damage over time and decrease their armor by 1 for every second they stand in the area. The armor reduction lasts for 5 seconds while outside of the skills effect.
Comment: the option when you want to go with a damage ability. Its more or less a bladestorm without magic immunity but with a armor decreasement over time which can be countered by microing the unit. The armor rediction is a supportive component of the skill, amplifying attacks of allies.
Resume: I would go with a support route with the hero. I have made a huge analysis out of that so somebody can learn on an example how to look for fitting abilities. Always think about:
What do i want to make?
What playstyle does my current kit incetivate?
Is my kit consistent with the game and the hero itself?
Hopefully i could help there.