I'm in Hell (オレは地獄に居る, Ore wa Jigoku ni Iru) is episode 345 of the Naruto: Shippūden anime.
Obito is tended to by two artificialhumans, who help in his rehabilitation, while also telling him about Madara's goal and annoying Obito with potty humour. Through months of intense rehabilitation while also recalling his time training with both Kakashi and Rin, Obito recovers and gets used to his new artificial body parts including his new right arm. One day, White Zetsu arrives with news of Obito's team-mates being in danger, surrounded by Kirigakure-nin. When Obito fails to break through the rock blocking the exit, Guruguru offers himself as an armour for Obito. Obito draws power from the Demonic Statue of the Outer Path to break the rock. Madara tells Obito he will properly thank him in the future, and that Obito will come back to him despite Obito insisting that he's leaving for good. On his way to the battle site, Obito has a vision of Rin through his empty eye-socket but simply dismisses it as nothing. He arrives just in time to see Kakashi run his Chidori through Rin's chest with Rin whispering Kakashi's name before she dies. Rin's death awakens both their Mangekyō Sharingan. Kakashi passes out, and Obito proceeds to massacre the Kiri-nin. Somehow, Obito manages to draw an enormous power from within himself, using Wood Release: Cutting Technique, and while manipulating his new Mangekyō, seems almost impossible to beat. After the last Kiri ninja falls, the remaining ninja having been impaled on trees that he created, Obito disregards an unconscious Kakashi on the ground, and tends to Rin. Deactivating his Mangekyō, Obito stares at the scene and while grieving for Rin, grimly concludes that he is in Hell.