You'll be surrounded in this map and you have to defend the area for 11 turns with only a maximum of 10 units. There are three contraptions you can use here; two ballistae, and a fire orb. There are also 4 villages you can visit. The nearest house to the NE will give you a Master Seal, the house to the NW will give you 10000g, the house to the east has a Dracoshield, and finally, a Dual Club from visiting the house to the west.
You need to prevent the Hoshidan army from breaching the green tiles to the north. In the other hand, two of Takumi's retainers, Oboro and Hinata will be leading the troops from the east and west sides respectively. Finally, Takumi himself is stepping on a dragon vein. If you managed to defeat him, you'll get the Elixir he's carrying.
For the strategy, you need to set your most powerful and sturdy units so you can visit the villages outside your base. Silas, your avatar, and Effie will be your most reliable vanguard units here. Leave a handful of defenders at the base, preferably those who can operate the turrets. You can leave Odin and Niles to help man the contraptions. You can leave Azura at home so you can use her Sing command to the turret operations to get another shot. The some portions of the partitions in your base can be broken so take note of their positions and prepare to send one of your melee units to deal with the attackers in case they break through. Surprisingly, enemies will prioritize taking down the partitions first. Ranged attacks behind these partitions are quite effective.
Start by sending Niles to the ballista to the south and use it to damage a couple of fighters or spear fighters within range. If you have a Javelin for Effie and/or Silas, you can use those to safely take out the damaged Hoshidans approaching your base. On the third turn, Camilla, along with her retainers, Selena and Beruka will arrive as reinforcements. Selena should be enough to guard the NE ballista and take out the enemy archers attempting to use it.
Beruka and Camilla will give you excellent range to deal with any of the forces you've weakened with your turrets; not to mention that they're both axe wielders, which are stronger compared to the naginata the spear fighters and sky knights are using. However, be careful of the enemy archers since they deal bonus damage to fliers. They can also use the any ballista they get their hands on (be wary of your NE flank) In the other hand, ballistae can instantly bring down the HP of enemy fliers to 1.
More archers will arrive from the west and more fliers will appear from the south. At the 6th turn, Oni Savages will arrive from the boat on the SE and from the west. On the 7th turn, Takumi will use a dragon vein to dry up the docks and allow foot soldiers to traverse the dry ground to reach your base faster. This can also be to your advantage since your ground units can use this terrain as well. On the 8th turn, watch out for the large group of reinforcements coming in from the south since their objective is to break past your defenses. If you haven't saved at this point, I suggest saving now. If you're planning to take out Takumi, you should do it on this turn as well. Keep your defenses up; if you're playing in Classic mode, make sure that none of your characters will be endangered during the enemy's last phase in Turn 11.