Trying to find a Japanese horror movie

Hi everyone, I’m trying to remember the name of a Japanese horror movie (I might be wrong about the country, but I think it’s Japanese).

In the movie, there’s a boy who wears a charm necklace that he’s not supposed to take off. When he does take it off, he starts seeing spirits and gets really sick (like convulsions).

There’s a girl who helps him, and he likes her.

At one point, her friends go on a trip to a sort of isolated place (maybe with some ritual or supernatural significance). The boy isn’t invited, but he sees the trip paper/flyer fall out of the girl’s backpack, so he goes along secretly.

During the trip, her friends lock him in something as a joke, and after that really weird and supernatural things start happening.

The movie starts normal but gets spooky and intense when they reach that place.

Does anyone know what movie this could be? tu NN no ,