Silver-Colored Memories (銀色の記憶) is a bonus story released with the Bluray of Washio Sumi's Chapter - Soul. It takes place during the events of Washio Sumi is a Hero and features Sumi and Sonoko helping Gin prepare a birthday present for her younger brother.
The story begins with Minowa Gin practicing her combat skills in the training grounds. She later tells Washio Sumi and Nogi Sonoko that, according to her, she can be the most useful by being the team's melee fighter (since she is neither studious like Sumi nor a good leader like Sonoko). Gin's brothers, Kintarou and Tetsuo, interrupt their conversation by being noisy, but Gin is able to distract them and calm them down.
Some days later, Sumi notices that something is troubling Gin. When she and Sonoko ask her why she looks serious, Gin tells them that Tetsuo's birthday is approaching, and she can not think of a present to give him. The three of them decide to go to Ines to look for a present, but everything there is much too expensive for an elementary-schooler to buy.
Sonoko then suggests that instead of buying something, each of them make something themselves to give to Tetsuo. After meeting in Gin's room and discussing several ideas, they decide on three things: a kendama from Sonoko, a board game from Sumi, and a picture book from Gin.
Gin's story is called "The Three Little Goat Friends". It tells of three goats who were good friends: one is serious and diligent (called "Serious-san"), one is sleepy and carefree (called "Carefree-san"), and one is rambunctious and lively (called "Naughty-san"). Even though Naughty-san has trouble finding food, she is thankful that her friends are there to help her. One day, a wolf comes to the mountain where the goats lived and attacks them. The three goats find a cave for them to hide, but only two of them will fit. Naughty-san sees this as her chance to help her friends, and pushes them into the cave and seals the entrance. Naughty-san is able to chase the wolf away, but is badly wounded in the process. Her friends scold her for behaving so recklessly, but she tells them that she only wanted to protect them because they're her best friends, and she would do anything for them. And so, the three little goats lived happily ever after.
Tetsuo is very happy upon receiving his presents. The kendama, although homemade, looks just as if it were store-bought, Sumi's explanation of the board game excited him, and he liked the picture book as well. Gin tells Sumi and Sonoko that she is glad she met them, and she hopes that the three of them will be together forever.