The difference between a knife and a Chidori/Raikiri is simple. A knife will do your average stab relative to the size of the knife. The Chidori/Raikiri is a large explosion of lightning energy at the palm of the user's hand that is being shoved into the body cavity of the target of which its ultimate intention is a guaranteed fatality. A regular person can shrug off a knife wound depending on the area or at least will bleed to death if there are major organs affected. A (normal) person being ******** by a Chidori/Raikiri is guaranteed dead. It was deliberately designed by Kakashi to be a goddamn execution technique.
Basically if you're using Chidori/Raikiri like a knife, you're doing it wrong. Its supposed to be a condom for your arm made of lightning that you use to ******** your enemies through the heart. Sure you could always stab a guy in the heart with a knife, but it'll be considerably more effective if you punch them with a fist of lightning instead.
Ever notice that whenever Kakashi uses Raikiri, he deliberately aims for critical areas like the head or the heart. Like you're supposed to do. Sasuke seems to like to swing that s**t around whenever he's not setting things on fire.
(I'd normally double triple fact-check this statement like I would any grandiose statement because OCD but ******** Sasuke.)
As for the basic Rasengan having nonfatal combat results, that's why its incomplete. This is why the Rasenshuriken destroys biological mass at the cellular level. At least that's what it did when it mattered. Now its all about Biju bombs which is essentially a derivative of a final form of the Rasengan.
Jin_of_the_thunder
why can't a ninja just increase the sharpness of a blade is the situation calls for it.
Because that's something that samurai (and Sasuke at one point
with the Chidori) have a tendency of doing.
p***s extensions.
High-frequency blades, son.