Natsume, Kitamoto and Nishimura take a trip to an old inn to spend some time doing their homework. Surrounding the inn there is a lake; in which is believed to live a mermaid. Does mermaid blood really give eternal life?
Tropes associate with this episode:
- Childish Pillow Fight: During the montage, Natsume and his friends engaged in one with pillows and feathers flying everywhere.
- Delayed Reaction: It takes Natsume a few seconds before he realizes that Nyanko has stowed away in his bag.
- Hidden Heart of Gold: Even though Sasafune has constantly tried to attack Natsume and even wanted to kill Chizu, she did care about Chizu and wanted to be friends with her when she was a little girl.
- Humans Are Bastards: Sasafune firmly believes this since humans in the past have sought mermaids out for their flesh and blood, which grants them immortality.
- Hypocritical Humor: Nyanko says that Natsume has bad manners for not offering some chips to him, but when he does offer, Nyanko eats all of them.
- Identical Grandson: Keiichi's grandson looks just like him. When Chizu first sees him, she's convinced that she made him drink mermaid's blood.
- Ill Boy: Keiichi used to be very frail when he was younger. The reason why Chizu wanted to give him some mermaid's blood was so that he wouldn't die.
- My God, What Have I Done?: Chizu spends the entire episode and most of her life thinking that she robbed Keiichi of a normal life by making him drink mermaid's blood.