As marty already pointed out, there is still some confusion about IFR/VFR and IMC/VMC. Nothing in the set of Instrument Flight Rules says that visual cues shall never be the primary method of, for example, navigating to a runway. After all, that's what a visual approach is.
so i wonder why visual approach is IFR.
Because it wouldn't make sense for it to be a VFR procedure. If you're flying VFR, you're already on one big visual approach (of sorts; you just don't have the runway or a preceding aircraft in sight at all times) to your destination since you must remain in VMC at all times.
With IFR, however, that's not the case. They will be using navaids or following vectors from the moment they depart up until they reach the terminal area of their destination. If the weather is VMC, they could save the controllers some hassle of getting them setup for an instrument approach by just proceeding visually to the runway. Hence why the "visual approach" procedure was created for such situations.