anyways.....he wasn't scared but Itachi had pose a major threat, he could take out obito quite easily since he also possess a sharigan and knows about IZANAMI, something obito wasn't seen doing at all. Also do you think that everyone would team up to take out Itachi, Kisame would have betrayed his orders, since he had a close relationship.......Maybe Konan would interfere in this war also
why do people think Izanami is the solution to everything?
Obviously Obito knows about it if he knows about Izanagi. Madara said he taught him the Uchiha Kinjutsu(which includes Izanagi, Izanami, and everything else)
Itachi didn't learn Izanami on his own. The clan most likely taught it to him. He even said that Izanami was made to counter Izanagi, so many people from the Uchiha know how to do it.....
Kisame joined akatsuki because he trusted in Obito. Obito told him he would create a world with no lies and that's why he joined in the first place.
Kisame killed himself in order to protect akatsuki's secrets.
He's the most loyal of all.