In The Blood Summaries - Act 1: Shadow
Chapter 1 - Duckling Row - (AO3 Link)
Sasuke receives a genin team to train and complains to Naruto about it, and is given one last chance to gauge their skill in the form of a mission in the Land of Rice. He then goes home to complain about it to his wife, Ino, and his youngest children, Inou and Karai. Inou gets in some trouble for reading a comic book and is sent out to train as punishment. The next day, Sasuke meets with his students: the fanboy Kyou, the sensible Sunao, and the scared Go'on. He goes over the mission with them and they start their training for the day, and depart the next morning. They reach their destination, the village of Tamina, two days later, their pace somewhat hampered by Go'on's slowness. The mission is to help the village and its people clean up and rebuild, as a landslide had destroyed it earlier. Over the course of the mission, Sasuke slowly grows to tolerate, and even like his students a little. But at the same time, he's set on edge by things seen out of the corner of his eye, which turns out to be a child with his brother's face.
Chapter 2 - Preying Bird - (AO3 Link)
Sasuke meets the child face-to-face as he and his mother bring dinner to him and his team one evening. His name is Honbo Yakata. Sasuke finds himself obsessed, and begins following the boy around and observing his behavior. His movements and facial tics are almost identical to Itachi's, and he exhibits both mental and physical quickness as well. Yakata eventually notices Sasuke following him and speaks to him while Sasuke watches him from a tree. He nearly asks Sasuke who he really is, but is interrupted by Kyou screaming for Sasuke's help. Forced to leave his perch, Sasuke goes to see what the matter is and finds that Go'on has climbed up a very tall tree in a panic. Sasuke climbs the tree to get Go'on down, and ends up waiting a while as Go'on calms himself. During this time, Sasuke comes to the conclusion that Yakata is Itachi's son, and that Itachi is somehow still alive. He resolves to meet with Itachi after he and Go'on descend the tree.
Chapter 3 - Vulture's Feather - (AO3 Link)
Sasuke makes his way to the Honbo residence and asks to speak with Yakata's father. He is out of the house, so Sasuke waits and ends up speaking with Yakata a little while his mother makes tea. When Yakata's father finally arrives, Sasuke finds himself mistaken: he is not Itachi, not even remotely. He leaves the house in rage and shame, and mentally beats himself up all night for thinking such a thing was even possible. He and his students leave early the next morning, and they make it to Konoha by the evening, Go'on's mood and stamina greatly improved. Sasuke tells Naruto that he intends to keep his students when reporting the completion of the mission, and returns home, resolving to never think of Yakata again.