Like, a samurai who did something really cowardly/dishonorable and is cursed to be undead? I guess you could just make a graveknight with a katana and samurai armor but I'm wondering if there is anything more specific.
Some outsiders could fit. Thoxel demons, several kinds of oni. Heikegani almost certainly aren't what you're after, but they are very specific to samurai. I can't think of or find with a quick search specific undead for you.
There are a couple of undead templates that could work. Jiang-Shi vampire has an eastern flavor that seems like it would fit. You could also go with a ghost. If you are looking for something fairly basic skeletal champion or zombie lord would also work.
Shenzuzhou can be reflavored easily for this purpose. Just give it traditional samurai weaponry.