First, run down the path and make a turn at the first left where there will be a blue orb fragment. Then return to the left part of the fork in the road and face off with the Goatling, being sure to evade the blue flames sprouting from the ground. When you beat it, run along the left wall (from Dante’s perspective when his front is facing the viewer) look for a small set of double doors which holds a Secret Room. Now enter the grand door with the red orb in front of it where you will be greeted with a cutscene.
With its thick skin it is hard to harm this monster with your starting weapons. It uses its large arms to strike at enemies and it can latch onto the ceiling and climb to another area to perform an attack. They will try to smash their enemies with their weight or throw you. Though this is hard to have happen, if you attack its arms, you will cut one arm off, making the beast much easier to fight.
A good way to get rid of him is shooting at him from a distance, and constantly avoiding his jumps. Also, you might want to stay away from him when he hangs on the ceiling, to avoid his stomping. When the Msiras start appearing, focus on the Orangguerra to finish him quickly.
Reap the key once you win against Orangguerra and enter the door with two angels which ends the mission.