Sonoko in Reminiscence (追憶の園子) is a bonus story released with the Bluray of Washio Sumi's Chapter - Promise. It takes place after the events of Washio Sumi is a Hero, in the year 299 of the Divine Era, and centers around Sonoko's life in the Taisha's care.
Enshrined in a room administered by the Taisha was Nogi Sonoko. As a result of using Mankai 20 times, she lost most of her bodily functions and is confined to a hospital bed. As she releases some of her fairies, a Taisha priest enters the room. She is annoyed by the formality of his introduction, but concludes that there is nothing she can do to change it, telling herself, "It can't be helped."
Sonoko recalls how her parents reacted to their daughter's current state. Her mother wept, and her father, though trying to reassure his wife that this sacrifice was necessary to protect humanity, was clearly distraught. Because of this, Sonoko tries to act cheerful to ease their pain, saying "It can't be helped."
Since Sonoko receives treatment similar to that of a god, she has been able to learn many things kept secret from the public. She knows about the heroes from the Anno Domini Era, and how their fight eventually ended in a 300-year armistice and the destruction of everything outside Shikoku's barrier. She knows about the terrorist attacks that took place around the beginning of the Divine Era, and how the Akamine family was able to quell the chaos that ensued. After pondering the bits of history she has gathered, she wonders if the gods (those of both heaven and earth) care about humans at all, or if they're simply just using them as pawns.
Time passes, and Sonoko tries to imagine her friends, Minowa Gin and Washio Sumi as middle-schoolers. She asks the Taisha priests if she can see her friend again, but is rejected for undisclosed reasons. Sonoko does not understand why she is forbidden to see Sumi, since the Taisha is willing to fulfill any other request, but she relents, telling herself "It can't be helped."
On November 10, a Taisha priest informs Sonoko about the selection of the successor to Gin's terminal, and that one of the remaining candidates is Miyoshi Harunobu's younger sister. She is intrigued but feels sorrow for both Harunobu and his sister. Gin's birthday also reminds of her desire to see Sumi, and begins making outrageous requests for the Taisha. She is disheartened when the Taisha is able to fulfill all of her requests, but still denies her permission to see Sumi.
As Sonoko is alone in the hospital room with her fairies, she eventually breaks, screaming about the unfairness of her situation, the apathy of the gods, and her overwhelming feelings of helplessness. Afterward, she realizes that nothing will change, and stops asking to see Sumi. She recalls the time she spent with Sumi and Gin and notes that the memories she has are more precious than anything the Taisha could give her.
- Some of Sonoko's fairies are named here, including Ryoumensukuna (nicknamed "Sukucchi"), Daidarabocchi (nicknamed "Dai-kun"), and Gashadokuro (nicknamed "Doku").
- This story includes the reveal of Gin's birthday, November 10.