After all these wild these wild theories, I constructed one myself.
Kakashi acquired his MS when Tobi did. Or, vice versa. Think of it like this, A random fodder gets his sharingan stolen then he awakens MS. Will it evolve in the other eye aswell?
Kakashi acquired his MS when Tobi did. Or, vice versa. Think of it like this, A random fodder gets his sharingan stolen then he awakens MS. Will it evolve in the other eye aswell?