You might be thinking until now, who offered to attack from the Fourth side?! Well it obviously isn't the two illustratian ladies, they have no powers even if they wanted to attack. Their only form of help can be financial, and even that has its limits. Getting to the point, Commander Alia offered to attack from the fourth side.
Just to describe the three other sides first, one will come from the right side which will be from the Platoon coming from Bale Town. Although not the main attack, their contribution in this battle is the second biggest, quantity-wise. Pameres Kingdom will face them straight ahead with 200 Guards, nearly 300 if the Platoon from Gaster Kingdom manage to arrive in time.