That's about where the story ends.
Yeah, Japanese folklore takes the "keep it simple, stupid" approach to spooky bullshit. They just ask you to imagine a samurai staring down at some guy mooning him with an eye up his ass, and make up your own ending.
Variations of the theme might replace the Shirime with a snake-necked woman, or a woman without a face, or a chick with a slit mouth, or that thing from Pan's Labyrinth. Basically, give somebody eyes where they wouldn't usually have eyes, and make them chase a samurai around, and you've got a Japanese ghost story.