A rare addition to his hero outfit, Deku is seen wearing a colored scarf in recent manga chapters. But why does Deku wear a yellow scarf?
Deku chooses to wear a yellow scarf because Gran Torino gave it to him. After Deku decides to leave U.A. and hunt the League of Villians on his own, he stops by Gran Torino’s hospital room and receives the yellow scarf.
Gran Torino shared some advice about how to best handle Shigaraki and the League before handing the scarf over.
Deku is discharged by his doctor
In chapter #309, Deku has begun the process of becoming discharged from the hospital. The Paranormal Liberation War has calmed down, and a large number of patients have already been treated thanks to Recovery Girl and cutting edge medical equipment.
A doctor reminds Deku of a previous warning that extreme injuries could leave his body immobilized. Deku was able to use his quirk to reinforce his limbs from inside out to keep them from shattering.
It’s at this time that Deku informs his Mom and All Might that he’ll be dropping out of U.A. Shigaraki has the ability to track him down, so no moment at the school would ever be safe. If Shigaraki were to reach full strength, he’d cause even more damage than what’s already been done. Deku considers it his duty to drop out of school and take down Shigaraki and All For One before that happens.
All Might says he can’t stop Deku from going, but at the very least he’s willing to follow Deku and look after him. In the past, All Might made a promise to Deku’s mother to train and protect him. As All Might continues getting weaker, it’s important for Deku to be prepared to replace the Symbol of Peace.
Gran Torino gives Deku his yellow scarf
Before leaving the hospital, Deku makes a stop by Gran Torino’s room to check in on him. He’s laying in a hospital bed with a bandage around his head. Otherwise, Gran Torino seems alright.
“I should’ve made the kill, sorry,” Gran Torino says as he hands Deku his yellow scarf. “Don’t be so rigid. Killing can be another way to save someone.”
Gran Torino tells Deku to never forget that. Yet, either way, he needs to destroy the League of Villians.
Deku then covers himself in the yellow scarf and wears it while doing hero work alone.
So that’s the answer. Deku chooses to wear a yellow scarf because Gran Torino gave it to him. After deciding to leave U.A. and search for Shigaraki alone, Gran Torino gives Deku his old yellow scarf to wear.