Huh. Is she supposed to guard Kanna so that Kanna accomplished her goal in the future? I figured she has other roles as well but I guess that one is plenty important anyway when we are talking about a super powerful being coming back :D
You are correct: Shimiko's first job is to protect the space/time continuum (if that gets invaded, everything gets fucked, since most creatures don't know how to properly time travel so their actions blend into time, instead of cause all hell to break loose.)
Her second is to act as one of the guardians of the seal (there are seven seals) to the Dark Horse, and her third job is to protect Kanna, and the other Guardians. They all are supposed to be guardians of each other--which she has the burden of knowing she failed that in the waaaaay back past (but, she did become a guardian at a very young age.)
If I ever finish Dark Horse, the second series goes into what happened to the other guardians. They are all supposed to be immortal like Shimiko--at least, physically immortal (they can be killed,) and the end of Dark Horse introduces the character responsible for those deaths.
Ah. I guess having one seal right beside you is pretty convenient then but also makes you a constant target. However, Kanna is a target regardless since she is THE threat for the Dark Horse and its underlings.
All in all, attacks will happen so I always found traveling with the seal to be more effective than locking them up in some temple or inside another sealed location hoping the evil never gets there. Because it will. Always :D
Or the seal just gives up on their own...
Also, 1990s ennui.