I recently got a knife as a gift and after only using it two times it has started to rust, despite making sure to properly clean it and dry it after using it. There is also one large spot of black/blue discolouration on the back of the knife. Also I'm not sure if this helps but the branding on the knife says 'Okeya'. How can I avoid this happening and what should I do to treat the rust? [![enter image description here](https://i.stack.imgur.com/mEjO5.jpg)](https://i.stack.imgur.com/mEjO5.jpg)