The choice of plan is obvious: Encirclement. Your knights break in to two separate groups and rush forward to either side of the human force. The group of soldiers yells and partially turns to face your troops, having to rapidly adapt to this new situation. With your appearance, their odds have notably worsened. Rapidly assembling in to a battle line less than ten meters away from the flanks of the foe, you await with anticipation for the primary force to crash into the enemy's front. The ones you're looking at dare not break formation, lest they leave their allies without a reserve and themselves vulnerable to being rolled up by the Barnin-Tra. Before they can make that mistake, your ally's force arrives, mere seconds after your own. In a great tidal wave of flesh and metal, the two fronts meet, the Royal Guardian being clearly front and center. Still, even they cannot fight off an entire army.
Your forces break into action themselves when the first cry of pain enters the air from a wounded or dying human. Galloping forward the last, short distance, they leap upon their prey with ferocity and intent. Blood flies immediately as their swords slash down upon the ready foe, breaking past guards and slipping through attempted parries to gut the resisting humans. The enemy is outclassed, and even if they could devote their entire attention towards you, they would still be in for a hard time. As it stands, this is a slaughter.
It is, however, one that is something of a slog. Although quick maneuvering and a perfectly coordinated attack keeps the enemy off balance, their line remains formed up, if a bit thinner than before. You don't outclass the enemy by that much on an individual basis, and they are willing to fight to almost the very last soldier. They cut down many a Barnin in retaliatory strikes, blades of various weapons penetrating through the gaps in the natural carapace you possess if not simply smashing past it outright while the Tra at the front get cut down in vast quantities by the member of the Guard. They are textbook, elegant in their heavy armor but with no less strength for their grace. While they can only do so much, this level of casualties is certainly more than a little worrying.
You nod at the two Yun next to you, and change course. Forging a path through the mass of humanity is tricky, but far from impossible. You use your blade to keep the humans before you on the defense, while using your razor-sharp legs to slice through the armor and flesh of the ones directly in your way. After a handful fall to your wrath, the rest stay out of your way, while your two soldiers continue to guard your flanks desperately from those who would intervene.
A shouted warning alerts the Guardian just in time, and the warrior turns after removing her axe from the torso of another fallen Barnin. The din of battle fades slightly as you close in, but you make sure to stay out of easy reach. It wouldn't do to be cut to shreds. Your opponent snorts derisively before speaking.
"You think you have a ghost of a chance against a member of the Royal Guard? Bug, I'll crush you and all your skittering underlings for what you've done." She seems confident enough, but her bravado shows that she's more scared then she'd like to admit. Time to test that theory.
You take another step forward as the battle momentarily slows for the pair of you. "I have many allies, you are but one human. I am sorry to say that your time is over. Have at you!" In a burst of motion, you and your two guards leap forth and bring your swords down upon her. A swift slice through the air keeps you away, but she can't be everywhere. Four Barnin-Tra charge at her back, and she continues her movement, swinging around to cut through two and deflect the arms of the other two with a gauntlet. Continuing to turn back around, she leans out of the way of your sword and that of one of your guards while slicing through the blade and skull of the other. The battle is now raging once again, but this is temporary. Then Elite Captain [Primary] comes in then, and brings his own weapon down. With the weight and speed behind it, the human can only lock blades, smashing the hefty sword in to the ground with her own axe. But this is your own chance. Taking another step forward before she can do anything, you lift up your frontal pair of legs and jab downwards at the back of her knees, vulnerable spots in the hefty armor. You manage to cut her lower legs clean off, and lever the flexible armor plates off to separate her from her limbs fully. Walking forward so that you stand over her, you put your sword to the back of her neck alongside your fellow as she lies down in the dirt.
You speak as one. "Yield."
These soft-spoken words cut through the battlefield as the humans cry in alarm when they realize what you've done. Although costly, your joint attack brought her down in the span of a few seconds. There was only so fast she could rotate. Almost immediately, the survivors throw down their weapons and surrender, the presence of the Guardswoman being the only thing that kept them from breaking. Out of 100 or so humans, only about 20 survive. Their own captain seems to have been killed by one of your Yun. In return, you have suffered about 15 casualties, and the infantry somewhere between 70 and 80. As Tra field healers tend to the survivors, the Tyrant [Primary] comes over to congratulate his two captains on a job well done. You have a few options here, and you believe you can influence your commander one of three ways.
[] Stay Put. Continue to stand guard here as ordered. If nothing else, you'll get some looting done, and you may find a way to open that mysterious box.
[] Fall Back and Report In. This mysterious box looks very important, and changes the situation. It would be best to take it back to a safe location, as the foe will probably stay away from this exit for now, and thus your objective is achieved.
[] Advance. You could enter the Castle and try to further aid your forces by striking from a probably unexpected location. Of course, it would only be you and yours doing this. The Junior Tyrant is willing to let you go, but isn't willing to commit his other forces to this (highly dangerous) mission.
So, what next for you, Guardslayer?