I had an important visitor, a friend for many moons visit, and she carried her Japanese knife. When it arrived, it was a mess, it was rusty and she was told that rust is not a problem. When a knife is rusty, it can cause many side effects, and it’s potentially dangerous.
One word, “tetanus” is one illness you really do not want to get but it is unlikely unless the knife is very rusty. The Rust on your knife are iron deposits made from pieces of the steel that have transformed into rust from water entering through tiny porous parts.
Most importantly, you need to clean your knife and so the best solution is to use Barkeeper’s Friend, or comet, powders that can be used to take off the rust. Use a sponge with that has one side with some abrasion, not the green type, and sprinkle it onto the knife and water it, and wipe.