Tanjiro and his wooden box are good companions to accompany Nezuko. But How Does Nezuko Fit In The Box?
Because her demonic ability allowed her to change her size, Nezuko could get inside the box. Depending on how much energy is used, his height and energy change. Because of his rest size, Nezuko can enter the box after the fight.
To protect himself, he may also change his height. This skill was valuable when Kanao was asked to follow Nezuko but could not. Nezuko’s bamboo muzzle also prevents him from demonic behavior.
The Story Behind How Does Nezuko Fit In The Box
When Nezuko attacked Tanjiro in Chapter 1, he started to change. His muscles and height rose with his strength, and he did not shrink until Giyu defeated him.
At Giyu suggestion, Tanjiro and Nezuko make their way to the home of Urokodaki Sensei. Tanjiro built an improved basket for Nezuko to sleep in during their trip.
“Nezuko. You made yourself turn into the size of a grown woman, right? Can you do the opposite of that and shrink?”
Tanjiro to Nezuko | Chapter #2
The two did not find another official ossuary of Nezuko until they reached Urokodaki. After Tanjiro won the Final Election and was sent on his first mission against the demons, sensei built a new box.
“This was the box I carried my sister in during the day. It is made with an extremely light type of wood called “Mist Cloud Fir.” After painting it with “Rock Paint,” the outer layer hardens, strengthening its durability.”
Tanjiro explaining the box’s upgrades | Chapter #10
Nezuko sleeps in a box to avoid exposure to the sun. He was as hot as any other demon, but he could stand outside during the day when it was very cloudy.
That’s all there is to it. Nezuko can change her body shape to fit the box at will. The size is determined by the amount of energy they need or have used before. He can also change the form to protect himself if necessary.