I could not find vanilla extract in my town. There is vanilla sugar instead in markets.In my cake recipe, there is  vanilla extract and it is whipped with egg, sugar and oil. But I am not sure with vanilla sugar.  On my first attempt I mixed it with dry ingredients, but the cake I made had too much crystallization. I wasn't sure if that was the reason.  Should I mix it with my dry ingredients like flour, baking powder and etc or with egg and sugar in the first step. ?   Thanks. 
Just glancing at the knife, it appears to be made with rough san mai technique forged stock or a similar form.  This is a technique were a soft iron or steal is sandwiched with a higher carbon hardenable steel center layer which is then honed and will hold an edge.   The outer layer is left rough and somewhat decorative, and though it is soft and cheaper metal, it actually adds to the durability of the blade by being softer.  However, it is porous and can tend to catch water, acids and corrosive items so could be prone to rusting if not sealed and yours obviously fits that description.  Vinegar as suggested, diluted, could well help clean off the rust, but be sure if you go that route to promptly clean any off and consider neutralizing it with a base such as baking soda.  As light a layer as you have, just a good wash will likely remove it though.  With any use of something like steel wool, keep it away from that beveled edge which should be you hardenable steel.  I would tend to suggest a good wash and then not only dry it well, maybe even use some heat to make sure, such as a blow drier.  Once good and dry, give it a light oiling as you would cast iron and keep it regularly oiled to keep a layer to prevent direct water contact.  Taking a look, I see Okeya knives listed as carbon steel and iron, never corrosion resistant.  I would never soak, use a dish washer, or leave wet at all or in contact with anything corrosive such as fruit juice. If you use oil, light oil and flavor neutral, that will not go rancid. 