In "Ishi Okoshi," Natsume meets a small youkai called Mitsumi in a forest. Mitsumi is entrusted to wake up the divine youkai "Iwatetsu" from its deep slumber. Mitsumi weighs on Natsume's mind, so he sets out to help Mitsumi with his task.
 
In "Ayashiki Raihousha," a mysterious visitor appears in front of Tanuma. Nearly every day, the visitor visits Tanuma, talks to him a little, and then leaves. Natsume, who knows the visitor is a youkai, worries for Tanuma, but Tanuma enjoys these exchanges with the youkai. The youkai means no harm, but Tanuma's health slowly starts to deteriorate.
 
(Source: Anime News Network)

When Reiko was Takashi's age, she bound the names of demons and spirits in her Book of Friends, enslaving them to her capricious whim. Now Takashi is the owner of the book, and the creatures will do anything to get their names back.
 
(Source: Viz Media)