Ishi No Kokoro summary:

Over 20 generations ago an army of soldiers, monks and alchemists gave their lives to seal away one of the world’s darkest secrets. In order to protect humanity, their souls were woven together to create a barrier, and their bodies turned to stone - preserved in time for their souls to return to should the barrier ever be broken. However the price was not paid by them alone- Now, centuries later, 4 youngsters variously affected by the curse, unwittingly stumble into this mystery...