After the tragedy during Rin’s death by the hands of Kakashi, Obito was so upset to see her lay still on the ground, leading him to go absolutely crazy and killing a bunch of Ninja’s from the Mist using his new gained Mangekyou Sharingan as well as play with his powers which he got from Hashirama’s Cells.
After he realized that the only thing he could do was to follow Madara’s orders and way in order for him to help Madara develop a Genjutsu strong enough for him to cast upon everyone pulling them into his own “Perfect” world. He described this to Obito in order to get him thinking that Rin will be brought back. Unfortunately it looks like endless hope and misery follows Obito.
The fantastic image above was drawn by the incredible YesimTekin. Go and check her work out as it’s absolutely amazing!