As I am sure you can tell by looking at it, your Japanese knife is primarily sharpened only on one side. As a result, the cutting edge is angled more steeply. Japaneseknives on Wordpress has some simple pictures illustrating this. This asymmetry is why you can't reliably use a honing rod on it, which relies on swipes to both sides of the edge to keep the blade smooth and free of burs.

The steeper angle makes the blade sharper, but you could say it is a double edged sword that can also make it prone to wearing more rapidly, depending upon how it is treated. As a result, sharpening only once a year may not cut it. There is another page on Korin's website that might be more helpful to you, including an informative video. L'Ohira's Knife Care & Sharpening page has some good tips on the type of kit you might want to use, including 3 grades of water stones, though you may or may not need the course all that much:

• Arato: A coarse grit stone used mainly for damaged edges and for creating new sharp edges.
• Nakato: A medium grit stone used for minor repairs and creating sharp edges.
• Shiage: A fine grit finishing stone.

Much of that information is also covered in the Korin sharpening video.
Also, since the knife is carbon steel, it can rust. Based on your question, it sounds like you probably take good care of your knives anyway, but you should especially make sure you clean this one promptly when dealing with acids.

Hone frequently, sharpen periodically

A proper, sharp knife will have a well structured, rigid, and sharp blade bevel (i.e. the very edge of the blade, less than a hair's length across, where the steel comes to a point).

No matter how hard the steel is, the bevel will wear with cutting so it needs to be maintained.

Hone yourself

Honing is the process of drawing the length of the edge along a surface to help maintain its alignment. Knife edges will thin, become ragged, and fold over themselves over time, resulting in a dull edge. By drawing your knife across a honing rod (NOT recommended for 60+ HRC knives) or a leather strop (or balsa, or newspaper on a hard, clean(!!) surface), the rod/strop will help realign your edge so that it is centered across the bevel, remains sharp, and is given proper structural support (triangles are strong!) by the bevel.

Hone often! Honing removes little or no material, and honing a knife before or after use takes just a few seconds and will help keep the edge and reduce the need for frequent sharpening.

Honing is easy to learn (YouTube it) and should be done by knife owners.

Sharpen professionally

Edges will eventually get worn as the steel takes strain from repeated cutting. The edge will get dull through folding, crystalline stress, and microscopic nicking. This cannot be avoided, but honing can reduce the time it takes for the edge to wear.

Once this happens, the blade needs to be sharpened through removing the old steel blade and reshaping it back to its original edge. There are many ways to do this through wetstones, drystones, sanding, grinding, etc.

You can try to do this yourself, but my strong advice (I'm a director of a high end knife company) is to send the knives to a professional sharpener instead. It's hard to get edge angles correct using home equipment, and a properly honed knife doesn't need to be professionally sharpened very often....once every 6 months with frequent use or once every year with less frequent use.

The sharpening period can change dramatically depending on the cutting technique, food products, knife geometry, steel quality, etc. A good way to tell if your knife needs sharpening is if it doesn't feel sharp anymore despite regular honing. That means the edge has worn and it's time to send your baby out for sharpening.

Professional cooks, of course, will go through knives faster because they cook with higher cutting pressure and more frequent use in the kitchen.

Know your bevels

Modern gyutos are NOT always single-beveled. For maintainability and for a global market they are often manufactured with symmetrical or slightly asymmetrical bevels. You should figure out whether your knife has a single, symmetrical, or asymmetrical bevel and write that down somewhere, so that you can let the sharpener know.