The following contains major spoilers for My Hero Academia Chapter 290 by Kohei Horikoshi, available now in English from Viz Media.
Dabi is most known for his role in the League of Villains, now the Paranormal Liberation Front -- a hero organization run by Tomura Shigaraki, My Hero Academia's main antagonist. Since the beginning of the anime, he has been in arms with the villains in the organization, wreaking havoc on professional heroes and the students of UA with his powerful Blue Flames Quirk. However, manga readers know there is more to Dabi than meets the eye.
Chapter 290, "Dabi's Dance," revealed the flame villain's past and confirmed many fan theories. Dabi's name is actually an alias; his real name is Toya Todoroki, the eldest son of Enji Todoroki, the #1 pro hero Endeavor. Toya was previously assumed dead, so when he revealed his identity, his presence in battle shocked his father and his youngest brother, Shoto. Toya Todoroki's beliefs and outlook on the world have changed drastically, but his physical appearance was what made the boy truly unrecognizable.
Dabi's Appearance in My Hero Academia
Dabi has a very recognizable look. His skin was burned as a child, as he lost control of his Blue Flame, and since then, the overuse of his Quirk has continued to take a toll on Dabi. The purplish-toned rotten skin is attached to healthier sections with a variety of staples and piercing rings, adding to Dabi's overall alternative look. Unlike the other Todoroki, Dabi's hair is neither white nor red but instead jet-black, distancing him even further from his previous family.
However, the most interesting disparity between Toya Todoroki and Dabi is in his eyes. After Twice's death, Dabi nonchalantly stated that he has been unable to cry since his tear ducts got burned, being offended at the suggestion of his emotions. Interestingly, symptoms of burned tear ducts include eye pain, blurred vision, dryness and of course, the inability to cry. This aligns with Dabi's current character design, as the villain's eyes often appear smaller than they are, as if he is squinting. Dabi likely has to squint his eyes to be able to see due to blurred vision or to minimize discomfort from any pain or dryness. This changes his appearance drastically from how he looked as a child.
How Did Toya Todoroki Look During His Childhood?
As a child, Toya looked very similar to his siblings. His skin was healthy and not burned, and his hair was completely white, similar to his younger brother Natsuo. Due to being born prematurely, Toya was smaller than his siblings Fuyumi and Natsuo, but after a growth spurt, he quickly became the same height as them. However, the most shocking difference is that Toya had noticeably larger eyes than when he is seen as Dabi.
In flashbacks, Toya's eyes are that of a typical anime child -- large, sparkling and emotive. This is completely different from the squinting and hopeless eyes of Dabi. As well as this, when he woke up at around 16 years old from his comatose state after accidentally losing control of his Quirk, the young Todoroki was still able to cry. Kohei Horikoshi's detailing around Toya's burned tear ducts truly turned the boy into Dabi, an unrecognizable member of the Todoroki family burdened with more trauma than ever.
Not having functioning tear ducts has forced Dabi to have dry eyes and blurry vision, so he has to squint his natural, large eyes to get by day to day. Dabi has become incredibly disconnected from Toya Todoroki and his old family, and Horikoshi's attention to detail demonstrates how his appearance makes Dabi seem like an entirely different person altogether.