Obito Uchiha, even though crushed under the rock near Kannabi Bridge entrusted Rin’s safety to Kakashi. But, unfortunately Kakashi couldn’t protect Rin and even ended up killing her.
But, why would Kakashi kill a comrade after witnessing Obito’s tragic end? Something isn’t right here, isn’t it? let’s dig a little deeper.
Why did Kakashi let Rin die?
Shortly after the third great ninja war, Rin was kidnapped by the ninja’s of the village hidden in the Mist.
The Mist shinobi’s later on sealed Isobu, the 3 tailed biiju inside Rin and had planned to unlock the seal as soon as Rin reached Konoha.
Hence destroying the Land of Fire! Kakashi on the other hand went to rescue Rin, he managed to rescue her, but was followed by the ANBU of the mist.