Aside from the obvious open parts for his shoulders and face, Grimnir's armor is made of a fine metal in one, solid piece. As such, Homura is unable to find any particular weakpoints in the armor, so instead she fires them all at the decorative golden part near his neck. As Grimnir is on the opposite side of the arena, he grins as Kotori charges him
"While I will admit your teamwork is quite abysmal, why I think the trickster himself would make a better partner than you two have."
Grimnir dances around, whipping the wind into a frenzy. His spear flashes through the air, slicing and stirring it. By now even the sandbags have begun to show signs of stress as the wind pulls on them. Grimnir slices horizontally, sending blades of wind to ricochet around the arena at his foes. In the midst of a storm like this, bullets find themselves unable to maintain their course.
Homura's first bullet manages to get redirected into grimnir's previously uninjured shoulder, he winces as the wound is immediately cauterized, but keeps up his loud mocking tone.
"I think you'll find my tempest to be more than worthy of judging you fools. Dying in battle is a great honor, one that gets you grand reward in the afterlife. Why, many would be overjoyed at the chance to perish, blade in hand."
With both arms injured, Grimnir resorts to kicking out with his legs in order to stir the tempest further. His maneuvers are precise and guided, lashing at the storm to sharpen and hone it, before long the sandbags begin to get cut by the violent storm, as are all unfortunate enough to be inside the GYM at this time. Grimnir, of course, gets minor scratches of his own, but his whirling movements seem aimed to keep him moving with the wind clockwise around the room.
"Your mistake is in presuming to control this force, such a wild, free spirited element of wind cannot hope to be controlled, you simply use it, drive it, manipulate it. Wind is a free-spirited and hopeful thing, your pathetic attempts make a mockery of the art."