Manga Spiritualist

[Illusion Knight]

I've had this idea for a manga for a while now, but I think I need help fine-tuning it, or maybe just a critical analysis from someone other than myself. Please bear in mind this is my first manga, so it's probably not the best you've ever seen in your life. Oh, and the names are entirely made up (I'm not very good with names and don't know Japanese well so they probably are where I need help the most). Any help at all would be appreciated.
PS: I just made a huge edit on this summary so it's shorter and more to-the-point.

The main point of the story is that in a Spirit Realm, where all spirits go after their bodies die, mysterious beings called Kinalians judge a spirit's deeds in its life, select and design an appropriate body for this spirit in its next life, and finally send this new body back down to Earth once one of the appropriate species conceives a child; the placement into a new body is enough to seal the spirit's memories of its prior life on Earth. But in the case of the Spiritualists, essentially humans who are entirely pure of heart and therefore have dense spirits, the Kinalians cannot fully seal the memories. But they don't realize this, and the being with partially sealed memories is sent down to Earth along with all the others. When their scouts realize the existence of a Spiritualist, the Kinalians do everything in their power to permanently seal it by deliberately killing the body and splitting the soul.

The main character of the story is a 16-year-old girl living in Japan named Tsukina Remoki, who is very tough (she takes out three gangsters, each of whom has a knife, as though it were child's play at one point) and hates acting sexy in any way. She is very cool and calm, nearly always thinking rationally and almost never truly angry (she believes that anger or any other strong emotion is the downfall of a great warrior). Her two closest friends are Miki Kunago, who is a year older than Tsukina and had helped her through school, and Koichi Sairu, who Tsukina once saved from almost certain torture and death. But Tsukina constantly worries about her dreams, in which she inhabits the body of one of her past lives (though she doesn't realize that the meaning of them is that she is a Spiritualist).

Eventually a Kinalian named Shigetoshi appears before Tsukina and tells her about the Spiritualists. He tests her strength, and when she cleanly defeats him, he tells her that he has been planning a coup in the Spirit Realm for quite some time and that she can assist him. He also tells her about the special abilities within the Kinalians, known as Soulseals, and teaches her how to use Soulseals (anyone who has seen a Soulseal can use one, and since Tsukina - as a Spiritualist - remembers the Spirit Realm, she can use them). Eventually, Tsukina (along with Miki and Koichi) go with Shigetoshi to stop the evil King and Queen Kinalians.