You're going to have a wonderfully fun time trying to hand sand S90V. CPM M4 is bad enough, Ive done that quite a few times, but I suspect S90V to be even worse. Even with 220 grit, a few strokes against the blade and the paper is killed. Makers that use S90V usually stop with a machine/belt finish and forgo the torture of a hand rubbed finish. Such wear resistant steels like that simply laugh at AlOx sandpaper. A better route is to use SiC paper, but only marginally. Like Bill said, if the scratches are deep, 400 grit may not be coarse enough. Heck, 220 grit may not be coarse enough!! Have fun with that.
When doing hand rubbed finished, you are on the right track. Alternate scratch pattern every grit change, to ensure you are erasing the previous grit. But I'm giving a bit of caution here, you'll have a rough go at it once you get past 220 grit. If it proves to be a lot of work, what you might do is get your scratches removes with whatever grit that takes, preferably lengthwise (tip to tang). Then if you want a finer finish, forget about alternating scratch patterns and just stay in the same direction and go up to 400, 600, 800, wherever you want to stop.