The Iga and Fuma both decide to gather the five books of forbidden techniques from the five villages. Iga wants them to find a way to transfer the Shinrabanshou from Miharu to someone else while the Fuma want them to find a way to eliminate the Shinrabanshou altogether. Meanwhile, Yoite wants to use Miharu for his own purposes.
So Yoite basically implants a part of his ki into Miharu and his friends, so that whenever he dies, they’ll all die too, in order to blackmail Miharu into learning how to use the The Shinrabanshou and grant his wish (which is to have never been born). Somehow by the end of the series, I have a feeling that Yoite will change his mind about his wish, and Miharu will probably find somewhat to save him from his fate from using the Kira.
Meanwhile, I’m growing increasingly suspicious of Kotarou, as his methods seem pretty ruthless and we don’t seem to know much about them still. I wouldn’t be shocked if he intends to use the five books to try to get the Shinrabanshou himself, and perhaps even already knows that there is no way to eliminate it. Of course, doing that would put Raimei in the difficult position of either betraying Miharu or betraying her village.