During the scene, the Yato will transform to the Omega Yato. In this point of the game, there's no need to grind for experience. You can move your army as a whole and head straight through the middle. There are several dragon veins that will reveal a healing area when activated. Use these spots to your advantage. Unfortunately, these healtiles are single tiles only so you can only heal one unit there at a time. Equip your best equipment, use your stat-boosting consumables, have your healers use your best and rarest staves for this final battle.
Once the battle starts, it will be hard to rush towards the middle since enemies will most likely outnumber your army and leave your softer units to be taken out during their turn. The rubble in the main area will prevent you from moving much, ground troops and fliers alike. However, these will also provide protection as well so use that to your advantage. Don't stretch too far and make sure to save your game so you can easily reload in case one of you units gets taken out very early in the mission.
The enemy berserkers and generals can deal huge amount of physical damage to your units. If you have fliers with you, consider taking out the bow knights and adventurers first then form a defensive wall that will allow your units to support each other. The best option is to fall back to the south a bit, while keeping your most powerful and sturdiest units to tank the damage. If you have area-of-effect abilities that reduce damage, increase damage, and heal, it will all be worth placing capable units within each other's range to complement these beneficial abilities.
Hold that position and let the enemies come to you. Once you have eliminated the first set of enemies in the middle area, heal up and push through north towards the defensive line of generals and sorcerers. Once clear, gather around Anankos while outside his attack range then gang up on him since you can't take him out with one unit alone.