While hunting mushrooms in the woods, the Yorozuya become infected with mentality-changing mushrooms while getting involved in a tragic war between a bear and a hunter.
When Catherine and Otose try to collect the rent, Gintoki, Shinpachi and Kagura escape to go looking for Matsutake Mushrooms in a forest. While Gintoki and Shinpachi are discussing a strange mushroom they have found, Kagura arrives carrying a wounded bear that has a mushroom growing on its head. As Gintoki and Kagura walk off, a giant bear arrives, and the gang plays dead. A hunter named Morinosuke arrives and attacks the bear, allowing them to escape.Marinosuke explains that the bear, named Masamune, is being affected by a parasitic mushroom from an alien planet. While having lunch, the four of them realize they have been infected by the mushrooms after Kagura cooks one in the pot. After Marinosuke is rescued from the bear, he tells the others his story and admits the bear is his own sin, and that he must kill the bear to correct it. Marinosuke deafets Masamune and leaves the mountain.
- Shiitake is a much lower quality of mushroom.
- There is a museum in Japan's Ibaraki Prefecture called "Professor Mushroom's Museum"which is dedicated solely to mushrooms.