I think the thing you mistook was the way they explained the spirits. Turbo Granny is a wandering spirit, seen or head of all across Japan, that's how her legend grew. The Location Bound Spirit is the one in the tunnel and was formed from the regrets of the girls who were defiled and murdered there. (also I'm almost certain there's a Japanese legend involving crabs, the Kani-no-Kami is known to be linked to regrets and pain if I'm remembering correctly. Why it was so dangerous is that Turbo Granny was already an extremely powerful spirit, but it merged with and became more when it came to pay respect to the dead girls, there it merged with the crab spirit and gained a lot more power. I'm still waiting for the series to finish to start reading the manga but I think this is what the crab is referencing.
I think the thing you mistook was the way they explained the spirits.
Turbo Granny is a wandering spirit, seen or head of all across Japan, that's how her legend grew.
The Location Bound Spirit is the one in the tunnel and was formed from the regrets of the girls who were defiled and murdered there. (also I'm almost certain there's a Japanese legend involving crabs, the Kani-no-Kami is known to be linked to regrets and pain if I'm remembering correctly.
Why it was so dangerous is that Turbo Granny was already an extremely powerful spirit, but it merged with and became more when it came to pay respect to the dead girls, there it merged with the crab spirit and gained a lot more power.
I'm still waiting for the series to finish to start reading the manga but I think this is what the crab is referencing.