In reality, nothing actually prevents rust on non-stainless steel, aside from continually making sure the blade is free of moisture, dirt, salts, acids and anything else contributing to corrosion. But, some things might slow it down a little bit. Your oil may or may not work, but keeping the blade clean & dry before oiling it will make the biggest difference. If the blade isn't clean & dry beforehand, putting oil on top of moisture, salts or acidic content on the blade will just trap it there, and potentially make rust a bigger problem. Even the salts in your skin oil can etch your own 'rusty fingerprints' into a 1095 blade (been there, done it).
If the oil is a natural food product (vegetable oil, olive oil, etc.), it likely contains some sugars, which break down to acids, and/or fatty acids that can contribute to rust, if not cleaned off and replenished regularly.
As I understand it, choji oil is just a mix of (mostly) mineral oil, with a little bit of clove oil added. Light mineral oil, by itself, is what makes up the largest balance of the 'rust preventing' products available today, and is the basis of why they work the way they do. In other words, simple mineral oil works as well as anything, for the most part.
By the way, the light grey/black oxide brought by the 'patina' on your blade will help to protect it, more than hurt it. Steel which oxidizes in contact with air (producing the grey/black patina) will be less reactive to the air + moisture that makes red rust. Scrubbing or polishing off the patina just makes it harder to protect the steel from rust. If protecting from rust is the goal, just let the patina be and keep the blade clean and dry.
David
