Tsuchigomori's Yorishiro

Tsuchigomori's Yorishiro is the source of Tsuchigomori's powers as a school mystery.

Appearance
Tsuchigomori's yorishiro is a small, round rock that easily fits onto the palm of your hand. It's rough and uneven, and Yashiro Nene even describes it as gross. Tsuchigomori claims it's a lunar rock, which is never confirmed nor denied.

In the anime, the rock is red, but in the manga, it's never shown in color. After it became a yorishiro, a black seal with red japanese letters spelling "封" or "seal" when translated to english was added to it.

History
Tsuchigomori's yorishiro was given to him by Hanako during his life as a human called Yugi Amane. Amane had brought the rock to the classroom, claiming it to be a lunar rock that fell from the moon. Amane said that the rock made him feel like he could go anywhere. He still ends up giving the rock to Tsuchigomori, saying "I've made up my mind now, I'm not going anywhere." Amane dies a few days after this, changing his future from what was written in his books.

Trivia

 * Tsuchigomori had already been a school mystery before Amane, which means that it's likely he had another yorishiro before the Lunar Rock, but it is unknown what it was.