Bright Smile, (危機に咲く笑顔, A Smile Amid Crisis in the Japanese Version) is Paralogue 21 of Fire Emblem Fates.
This paralogue is unlocked once Laslow has achieved an S-Support with a female character.
Subjective: The following part of this article is subjective to the editor's writing. Therefore, it may not work for everyone.
The map in this paralogue is quite large. The enemy occupies 3 corners (NW, SW, SE) while the player occupies the remaining (NE) corner. The player should consider bringing flying units (such as Beruka or Camilla), as not only is movement helpful, but there are many tiles that hinder movement; 'Woods' tiles slow the movement of units at many choke points, and there are two 'Lakes' in the center of the city that hinder efforts to regroup/reinforce. Azura is also quite useful, as she can use her 'Sing' ability to great effect in quickly reinforcing Soleil and her Lancers, and her Healing Descant is helpful in keeping your allies healed up in a choke point.
Laslow will inform the player to rush for Soleil and her mercenaries as fast as possible, and the game will also advise and notify you of two "Obstacles". These obstacles can be planted to restrict enemy movement; however, this simply makes them take another route, as you cannot completely block off one corner with one obstacle.
Losing the Lancers is optional (if the player is not interested in the rewards); Soleil will need to be reached quickly, especially if the paralogue is attempted near endgame as she will be severely underleveled until she uses her Offspring Seal.
All of Soleil's Lancers have Wary Fighter on them, so they will be able to survive enemy attacks for a bit; however, you should get to all of them quickly, as the enemy is guaranteed to overwhelm them otherwise, how fast they are defeated depends on difficulty and current story progress. Saving the Lancers will give you extra rewards at the end of the paralogue.
The majority of the enemies will be either Sorcerers, Heroes or Berserkers; however, in the northwest and southeast corners, there are three Dark Knights and Bow Knights respectively. On higher difficulties, the Dark Knights will have Lunge, while two of the Bow Knights will have Pass while the other one has Poison Strike.
Once you reach the middle, grab the obstacles and plant them in the southwest section, as the rest of the units will be able to reach the other two sectors easily. Hold off the enemy and their reinforcements, which arrive turn by turn and will come from all four sections of the map. Once all enemy reinforcements are exhausted, Zhara and his guards will move in on the player. On higher difficulties, Zhara will come with Countermagic, so it is ill advised to attack him with magic unless he can be taken down in one hit with it.
The script for this chapter can be found here.
If three lancers survive: Physic and Friendship Seal.