A Boy and His Erasers (少年と消しゴム Shōnen to keshigomu?) is the 5th chapter of the 9th volume and the 64th chapter overall of the Attack on Titan: Junior High manga, written and illustrated by Saki Nakagawa.
Eren and his friends are planning a surprise birthday party for Armin. When Armin learns that they plan on gifting him 100 erasers he tries to sway them into buying a new futon instead. When this proves too much he collapses from a fever and his friends notice his futon is broken from his attempts. When Armin wakes up his friends repair his old futon and celebrate his birthday.
Armin sits reading a book alone while his friends discuss something behind his back. Assuming they are purposely excluding him, he pulls out a listening device to eavesdrop on the conversation. He hears the group planning a surprise birthday party for him and figuring out food and drinks. When the topic of presents comes up it's decided on 100 novelty erasers to which Armin falls from his chair in shock. While walking home with Eren and Mikasa, Eren stops at a store and points out the erasers, stating they were like a status symbol with the more you had. Armin goes along with it but internally dreads the gift and wants a new futon instead.
The next day the group talk about which erasers to get when Armin stars loudly sneezing and mixing in a message for no erasers. During this his futon gets covered in snot and Eren goes back to the group. Thinking they got the message Eren returns telling Armin to ask his grandfather for a new one. Later in class Eren asks to borrow an eraser from Armin but he states he only uses pens and no longer has a need for erasers. Eren leaves shook and tells the party group to ignore any practical erasers; only ones that look nice but fall apart if used.
Armin continued to to change Eren's mind through presentations on how good a futon is but the hints flew over his head as the day before Armin's birthday arrived. The group go to buy the erasers but Armin forcibly tags along to thwart their efforts. They find a stationary store and Mikasa tries to lure Armin away but he resists. Just then Hange walks by with a cart full of erasers; Eren goes to the cart while Jean heads inside the store. Exhausted he passes out and the group rush him back home, Mikasa noticing his damaged futon. Inside his room everyone notices the futon merchandise and realize Armin needs a new one or he won't get better. The next day Armin wakes up and his friends repair his futon with supplies they bought and celebrate his birthday together.