In My Hero Academia, Quirks come in all shapes and sizes, from Tsuyu Asui's Frog Quirk to Katsuki Bakugo's explosive powers. They seem fairly straightforward, but then there are heroes like Fumikage Tokoyami, whose Dark Shadow Quirk seems to defy nature itself.
What are people supposed to think when a raven-headed boy can talk to a living shadow that emerges from his stomach? It's weird enough on its own, but fans have some startling theories about the true nature of Dark Shadow.
What Fumikage Can Do
The hero student known as Fumikage Tokoyami is an odd one, even by U.A. standards. For one thing, he is ordinary from the waist down, but he had a distinct raven head, complete with a beak and what looks like black feathers on his head. However, there are human elements mixed in too. For one thing, Fumikage still has human teeth, so he can talk and chew normally. He lacks human lips, but he can still articulate speech just fine. His "feathers" are actually dark hair styled like feathers, so he can comb or brush his hair like anyone else. It is the pro hero Hawks who actually has feathers on his body.
Dark Shadow is one of the few, if not only, Quirks that has a mind of its own. When Dark Shadow appears, it and Fumikage can talk to each other, and Fumikage gives commands to Dark Shadow like a commander, rather than using Dark Shadow like an unthinking muscle. Dark Shadow can provide tactical input, and it can even choose to retreat into Fumikage's body if it sees the need. It has a bird-shaped head like Fumikage himself does, and it has claw-like hands. But suppose Dark Shadow really was a person and not just a special Quirk?
The Twin Brother Theory
Mutation-type Quirks already exist, and some of them provide the user with extra powers. Mina Ashido's Quirk gives her horns, bright pink skin and black scleras, and Mashirao Ojiro has a strong tail like a monkey. In Fumikage's case, he has a bird head, and according to one fan theory, that and that alone is his Quirk.
If so, then his Quirk should be called something like Raven Head, and Dark Shadow is none other than Fumikage's long-lost twin brother, conjoined inside his body. If so, then the twin brother also has the Raven Head Quirk, but he also has an energy emitter Quirk that allows him to have so much power.
If this is the case, then Fumikage Tokoyami is two people in one. His "Quirk" is really his brother who is sent out to fight, and the brother is the one with the Dark Shadow ability. No twin brothers or sisters have been shown in the anime so far, so the possibility of twins sharing identical Quirks or even being inside each other cannot be ruled out too easily. Suppose Fumikage absorbed the other Tokoyami twin in utero, including his Dark Shadow Quirk?
According to the fan theory, if this never happened, then Fumikage probably wouldn't have qualified to enroll at the U.A. school at all. Fumikage would need more than the Raven Head Quirk to qualify for that school; it's thanks to his absorbed twin that he has the power to compete with the likes of Shoto Todoroki and Tenya Iida. If so, Fumikage owes a lot to the other hidden Tokoyami.