“Anankos couldn't possibly be defeated by Avatar alone. Realizing this, Avatar sets out for Fort Jinya to try and convince Hoshido to help.”
Traitor's Brand (裏切りの汚名 Uragiri no omei) is Chapter 8 of Fire Emblem Fates in the Revelation Version.
The script for this chapter can be found here.
On turn 7, a ninja with Locktouch will spawn at the bottom of the map where the party starts. If the chest nearest the entrance is opened, the ninja will exit the map.