One of the things that annoy me is when I find cups that are otherwise really nice, but through years of neglect and poor preservation, have ended up in a horrible state. This cup above is one such example, and it pains me because you can still see traces of the cup underneath - a soldier rowing his own boat up a river, symbolizing, I think, a hardworking soldier. That, and also because I've sold a cup like this before almost ten years ago
They're obviously not identical, but it's the same theme, and in fact, the faded cup seems to be nicer - the boat is in a better shape, and the soldier seems to be better proportioned. Instead, it's all faded.
The biggest culprit seems to be a simple cause, which is something no one should do, and that is to wash the cups with any kind of abrasive sponge/scrubber/detergent. I've tried it before - because the paint on top of the cup is usually from a secondary firing done at a lower temperature, and it's on the surface of the porcelain, it's quite easy to rub them off if you try. If you use a scrubbing pad or anything like that, the colors will fade really, really fast. Don't do it.
Instead, even if the cup (or bottle) is heavily soiled or covered in dust, just run it under water and use your fingers - that's usually good enough to clean the cup.
The second thing is even more obvious, perhaps - don't use them to drink sake, despite your inclination to do so. If you really must, because it is sort of cool, find one that isn't holding such a nice picture - use one of the more common ones, or ones with colors that are not likely to fade as easily.
Finally - be very careful with the flatter, sakazuki style cups. They chip really easily. On the flipside, the smaller, 2" chokos are quite damage resistant. I've had a couple fall from a table before onto a hard floor and somehow came out without even a chip. The sakazuki though, because they're so thin, chip quite easily.
So, I guess this is obvious, but worth repeating - don't use them, if you do, use the choko, and wash just with water and your fingers. That will keep your cups in good shape.