Fumikage's quirk grants him the ability to host a "shadow like-monster" named Dark Shadow within his body that he can materialize and de-materialize at any moment.
Dark Shadow is sentient and capable of speech. It exists as its own entity, and exists to serve its master regardless of the state it finds itself in. Fumikage can use Dark Shadow for a number of purposes. Dark Shadow is quick and can attack from afar, it can also defend at close range and its arms can be used to propel Fumikage and increase his mobility. Dark Shadow can stretch its limbs, giving Fumikage an advantage in close range combat. It can also hold physical objects for Fumikage.
Dark Shadow's personality and offensive power depend on the surrounding light conditions. Under strong light, Dark Shadow is small and weak in comparison to when its engrossed by darkness. Even so, Dark Shadow maintains extraordinary defensive skills, able to block attacks from quirks that create light like Explosion and Electrification. Dark Shadow is docile when exposed to light, making it easy for Fumikage to control.
Under little to no light, Dark Shadow becomes a large and ferocious beast with incredible offensive ability. One of Dark Shadow's claws was able to rip through dozens of trees with ease. It was also able to completely overwhelm and defeat Moonfish, a veteran villain, with a single strike. Dark Shadow's grip was able to break Moonfish's quirk enhanced teeth, which were able to pierce Shoto Todoroki's ice.
Dark Shadow's personality under the influence of darkness is the opposite of it when it's exposed to light. It is far more unruly and vicious and will attack anything that moves or makes sound indiscriminately.
According to Mezo Shoji, Fumikage's negative emotions (such as regret and indignation) intensify this version of Dark Shadow. Albeit at the cost of Fumikage losing all control of his quirk. Keeping Dark Shadow under control in this state is a great struggle for Fumikage and it requires all of his focus. Once Fumikage loses control, Dark Shadow starts enveloping Fumikage's body with its darkness and takes control over its host, with Fumikage slowly becoming immobile both physically and mentally. After taking over Fumikage, Dark Shadow can force its immobile host to move around.
Dark Shadow also has an energy limit, retracting into Fumikage's body when said limit runs out.
- Black Ankh (
深淵闇躯Burakku Anku?): Fumikage's special move (previously known as Tenebrous Abyss Body (深淵闇躯 Shin'en Onku?), he dons and equips Dark Shadow onto himself, wearing it like a suit of armor or an exoskeleton. According to Fumikage, equipping Dark Shadow onto himself mitigates his physical weaknesses.
- Piercing Claw of the Dusk (宵闇よりし穿つ爪 Yoiyami Yorishi Ugatsu Tsume?): Fumikage shoots out Dark Shadow's claw which attacks at great speed.
- Gloom of the Black Arm (黒き腕の暗々裏 Kuroki Kaina no An'anri?): Fumikage shoots out both of Dark Shadow's claws which attack at great speed and then uses Dark Shadow's claws to surround his victims.
- Like several other Quirks, Dark Shadow has its own signature sound effect: "CREEP".
- ↑ My Hero Academia Manga: Chapter 101, Page 14
- ↑ My Hero Academia Manga: Chapter 104, Page 6
- ↑ My Hero Academia Manga: Chapter 108, Page 13