The Gate of Kelves is Chapter 3 of Fire Emblem: Thracia 776.
The most important thing to focus on in this chapter is returning all of the children to their homes. Romeo goes to the upper left house, Corpul to the upper right, Lucia to the lower left, and Yuvel to the lower right. The children's names can be seen by checking their stats pages. Returning Romeo and Lucia will grant a shield ring and the Baldur scroll respectively. The other two will yield nothing immediately, but are arguably much more important as Yuvel will allow you to recruit Dalshien in the next chapter and Corpul will get you a warp staff in Chapter 7.
Luckily saving the children is not particularly difficult. The main thing to watch out for is the barbarians who will spawn from the western forest and attempt to destroy the houses around turn 10. Two will spawn each turn for around seven turns. Eyvel and two other sword wielding units should have little trouble dispatching them if they are already in place by the time the barbarians arrive. It is also a good opportunity to give EXP to Leif or Lifis. Also watch out for the Sword Armor Knights and Soldiers that will spawn next to the boss around turn 12. Once they and the enemies surrounding the children have been killed or captured, there will be no danger while rescuing the children and bringing them to their respective homes.
The two chests in the upper part of the map contain an Armor Slayer (left) and a Meteor tome (right). The bishop in the back will eventually use the door and chest keys in his inventory to take the Meteor tome out of the chest behind him and begin using it on you, so it would be easiest to get to and capture him before he has a chance to do so. With the Armor Slayer from the chest and Dagda's hammer, the boss should not be very difficult.
After defeating the enemies, it may be a good idea to use the storage house in the upper right to hold the extra weapons you may be carrying and the shop on the left to sell unneeded items. The shop also sells door keys, which you may want to start stocking up on now as they are helpful throughout the game and essential in the final chapters.
Before seizing the throne, it helps to give all important items to Leif and Lifis because of the units you have now, only those two will be usable for the next five chapters. First priority should go to the two scrolls and all swords you currently have. The coming chapters will not have very many to take from enemies, the only ones being long swords from the difficult to capture Sword Armor Knights, and most units you control will exclusively use them during the first three indoor chapters. Vulneraries are also helpful, but can be relatively easily stolen from the Soldiers in the next chapter so only one or two are necessary. This is also Eyvel's last usable chapter for most of the game, so be sure not to leave anything important on her.
The Village of Ith or The Pirate Isles
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