"How Come Until Now?" is chapter 600 of the original Naruto manga.
Summary
Kakashi and Guy are shocked, and start asking the once masked man whether he was truly Obito and upon seeing his Mangekyō Sharingan, Kakashi says that there is no doubt about it. However, Obito reiterates his point that it doesn't matter what they call him, and all that matters to him is his Eye of the Moon Plan. Kakashi flashbacks to the time when Obito died, and then asks whether he had survived the cave in, leading Naruto to ask them who the person in front of them was. Guy answers stating that he was a former classmate of theirs that was supposed to have died during the Third Shinobi World War. Kakashi, still in shock asks Obito if he had survived "how comes until now" shocked that his friend had not made this fact known for so long. Obito retorts that whether he survived or no, was unimportant, but if Kakashi had to have an answer it was simply because he had let Rin die. Even more devastated by this response, Kakashi asks him if he was going to blame him for that as well. Obito, however, says that it was pointless to do so, as this world would "disappear" soon enough. Naruto tries to rally his sensei, telling him that for right now, Obito's plan needs to be stopped. Obito uses the Fire Release: Explosive Wild Dance technique sending a giant vortex of flames towards his opponents. Kakashi unable to register what was happening simply stands there, despite Guy calling out to him. Naruto, however, intercepts the attacks with Kurama's tails. Before any side could act further, they are interrupted by Madara's appearance on their battlefield. Standing beside the younger Uchiha the legendary shinobi remarks that Obito seemed to be having fun.