Reunion (再会, Saikai) is episode 51 of the Naruto: Shippūden anime.
Yamato suggested that Sai's true objective in coming with them was to kill Sasuke, who, according to his master Danzō, was a threat to Konoha. Sai entered Sasuke's room, thus waking him. But, instead of following his orders and killing Sasuke, Sai revealed that he wanted to preserve Naruto and Sasuke's bonds. Sasuke expressed his anger at being woken up to be lectured on bonds by causing a giant explosion in his room, which attracted the attention of Sakura, Naruto and Yamato. As Naruto and Sakura met with their former friend, Sai declared that he was discarding his mission orders, and now wished to aid Naruto in bringing Sasuke back to Konoha.