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Chapter 73 is the continuing story from previous chapter, where Natori and Natsume have been asked to help search for the hidden study room of Hakozaki’s, a work by Yuki Midorikawa of Natsume's Book of Friends.
Natsume is shocked when he sees Natori is just behind him, meaning he heard about the Book of Friends. Natsume then asks Natori if he is willing to hear him out after they are done with the search. While they are discussing, Aimiya coming from behind, barely able to hear Natori mentions Natsume’s name. natori, fears for any inconvenience, lied to Aimiya that its actually Natsumeg, his new shiki still in probation. Natsume, who’s wearing a mask covering his face, shocked at the new name given for him, while Hiiragi and Nyanko-sensei silently giggled at the back.
Later, after Aimiya have left, Natsume remembers something that the granddaughter of Hakozaki’s mentioned earlier. She told them that Hakozaki had planted a maple tree for his granddaughter. Natsume deduce that if he planted the tree for his loved ones, then he must chose a room where he could always view the tree. With that in lead, they all went to search for such a room, finally finding one but had been badly ransacked already. The keen-eyed Natsume notices a small box with maple leaf wallpaper peeking underneath all the scattered things. Inside the box is actually a frame photo of the family, with a baby in the middle. Natori, looking at the photo, sees two dragons, possibly the shikis of Hakozaki’s, a light-blue colour and golden colour, in a protective-like position around Hakozaki. Realizing that the two dragons were acting as the guardian, both Natsume and Natori decided that they must instead find for objects shaped like dragons. They both then separate ways to search for the said objects. While being alone with Hiiragi, Natori asks her whether it is alright for him to hear about it. Hiiragi, knowing full well her master, just replied that that is better than sneakily trying to investigate. Laughing it off, Natori agrees with Hiiragi and wishing he is strong enough.
On the other hand, Natsume and Nyanko-sensei went to search for the dragon-like object. While passing the hallway, they heard that Nanase is there and seemingly found something at the northern building. Natsume, believe that Nanase might have found something, deciding whether he should go at the same direction or not when he senses something at the wall near him. Right after he asked Nyanko-sensei if he senses the same thing as he did, a door appeared on the wall, prompted Natsume for curiosity. In front of the door, there’s a dragon relief and when it notices Natsume had discovered it, the dragon blinked its eye. By that time, Natori and Hiiragi had already come rushing towards Natsume and Nyanko-sensei. The dragon at the door then came alive after blinking, claiming that Natsume smells something of his master. Natsume then took out the frame of photo from earlier, apologize to the dragon shiki for taking it without permission, but also thought of giving it to the granddaughter after the search.
Natsume then asked the light-blue dragon if he is Hakozaki’s shiki, also the whereabout of his study-room where he kept all his research. The dragon admits about being Hakozaki’s shiki, but decline to tell Natsume about the study room, since all this while, his master had been alone and abandoned by everyone, so he is not going to giveaway his master’s works. The dragon went telling that Hakozaki used to gather ayakashi everyday, summoned strange and interesting ayakashi with new spells, made unfair challenges and even cheated a large amount of sake from them. During sakura blooming, he also used to command all the spirits to clean up while he laughed coldly. It was quite enjoyable for the spirits at the time, however, whenever a sound heard from the main entrance, the master would rushed there to see of anyone coming, but only sighed disappointedly when no one actually there.
While the dragon is telling all these, the back door of the study-room, which the golden dragon is guarding were burnt. Since the back room situated at the northern building, it is possible that Nanase had set the fire. The light-blue dragon then angrily states that if they want to take the master’s works forcefully, then he will burn it all together, later vanishes from view. Both Natsume and Natori then rushes to the burning building, only to discover that the flames burning actually an abnormal flames. Nanase told that the flames are actually the flames of youkai and it would not burn the building.
When the building is burning, some papers flew from it, one paper smacking on Natsume’s face. Natsume whispers to natori about the papers, asking if they are still useful. Natori, seeing the spells written at the papers, realizes that those were some of the research papers by Hakozaki, frantically orders his own shiki to gather the papers. On the other hand, the angered Nanase left the place soon after empty-handed, thinking they had failed searching for the research. While they are looking at the flames together, Natsume finally tells Natori about his grandmother, and also about the Book of Friends.
After Natori hears the story from Natsume he comments that he is dealing with a troublesome thing by himself and he in turn replies that it is not troublesome with a genuine smile (probably recalling some of his interesting experiences and new friends he made along the way), on the other hand Natori muttered to himself that "such a thing" should be burned. (which implies how much he hates or sees youkai as a dangerous being rather than an equal)