The main protagonist of Yesterday Upon the Stair. He sees dead people.
- Adaptational Badass: Downplayed. While Izuku's quirk isn't much use in a fight, living with ghosts his whole life and having opportunities to help people that nobody else can have helped to put some extra steel in his spine even before Midoriya inherits One For All.
- All-Loving Hero: Averted. Midoriya is a very compassionate and empathetic young man, but he is not above resentment and bitterness, particularly toward Bakugou. Though he is disgusted with this.
- Amplifier Artifact: One For All acts as one for his original Quirk, allowing ghosts near him to interact with the world more. It's gotten to the point where, with One For All active, they become visible to others and attack others, seen best when Rei tackled Bakugou to the ground when he and Izuku were having an argument post-League of Villains kidnapping, leaving Bakugou to gape at her in shock.
- Bait-and-Switch Comment: Comes across as a Badass Boast but when Nemoto asks if he's scared, Izuku admits he's terrified, of what he's going to have to do to them.Izuku: You can still leave now. You don't have to die here. I don't want you to have to die. I get so little sleep as it is.
- Catchphrase: Often overlapping with Arc Words:"My friends are scarier than you are."
"Can't skip leg day."
"I lie to everyone."
"I'm sorry. That must have been awful."
- Chronic Hero Syndrome: Living or dead, Izuku can't leave anyone who he can help.
- Claustrophobia: Suffers from a terrible case of this to the point of only using stairs at the mall and begging and bribing Eijirou when the latter tries to pull him into an elevator.
- Combat Pragmatist: Becomes this under the tutelage of Shimura Nana, something that Aizawa approves of with the understanding that since your enemies won't be fighting fair, neither should you. Best shown during his fight with Muscular, where he hits Muscular with a groin attack, breaks his cybernetic eye and gouges out his regular eye with his bare hands since Muscular couldn't augment the muscles in those areas.
- Izuku partially breaks his right wrist to free his hand and bites Himiko on the nose for his plan to free himself and Bakugou.
- Conditioned to Accept Horror: Downplayed; Izuku has become accustomed to ghosts' Jacob Marley Apparel, but it still upsets him to think of what happened to make them that way.
- Creepy Shadowed Undereyes: With all the nightmares that come from dealing with ghosts, Izuku has these.
- The Darkness Gazes Back: Midoriya has tapetum lucidum, which makes his eyes glow like a nocturnal animal's in the dark (which tends to scare his friends when they're not expecting him), and pictures of him tend to have glowing red eyes. Dr. Tsubasa speculates it's a physical manifestation of his "invisible quirk".
- Deadpan Snarker: Izuku's has quite the dry wit at times, such as responding to Sir Nighteye's rather pathetic attempts to apologize with a dry, "Don't hurt yourself."
- Don't Make Me Destroy You: Izuku says as much to Overhaul and his minions, asking them to leave rather than make Izuku kill them.
- First-Name Basis: Eventually with Todoroki as they grow closer.
- Friendless Background: Well, living friendless background, with his only real friend until entering U.A. being the ghost girl Rei. When he finally gets living friends in U.A., he's initially unsure how to react, and is ecstatic when Kirishima refers to him as "our" Midoriya.
- Heterosexual Life-Partners: Implied he will be this with Todoroki, as they get older. The author has stated the two are (or will be) in a queerplatonic relationship, as, within the world of the story, Midoriya is aromantic and Todoroki is demiromantic.
- I See Dead People: His quirk lets him see and interact with ghosts.
- Magnetic Hero: Justified, as he has learned to play on people's emotions and make them like him, due to the number of hostile ghosts he has dealt with in the past.
- Momma's Boy: As in canon, Izuku is a momma's boy, though unlike canon he tells her about One For All (mostly because she already knows about his I See Dead People quirk and wouldn't buy him spontaneously getting a quirk like in canon).
- Nerves of Steel: Deconstructed. Izuku's experiences with ghosts and Bakugou have left him with great skills at compartmentalizing.
- Ocular Gushers: As with canon, he cries at the drop of a hat.
- Scars Are Forever: He has a noticeable scar over his left eye after his match against Todoroki.
- Slasher Smile: His smile is described as "like he's about to eat a baby" by Tsuyu, and Gran Torino acknowledges that unlike All Might, who wears his smile like a part of his costume, Midoriya brandishes his smile like a weapon.
- Stress Vomit: Happens after his incident with Shigaraki at the shopping mall and after being released from Compress' containment orb.
- The Unsmile: Izuku's "baby-eating" grin, first seen during the USJ incident and popping up multiple times later, is caused by him forcing himself to smile while completely terrified.
- Troubling Unchildlike Behavior: Living with ghosts all his life has left Izuku a little creepier than before. The various skills he's picked up helping them with unfinished business (like lockpicking), has Present Mic wonder about his possible Dark and Troubled Past.
- A side story details how ten-year-old Izuku got the bullies off his back after switching schools: he worked three loose teeth out while his class was watching a movie so that that blood would pour from his mouth in the flickering projector light. The entire class panicked and later voted him "most likely to be possessed."
- Weirdness Magnet: Ghosts tend to flock to Midoriya once they notice he can see them. Several have taken to haunting his home, turning it into a Haunted House.
- Why Did It Have to Be Snakes?: Izuku's claustrophobic ever since Bakugou locked him in a haunted closet when he was seven.
Izuku's best friend and Canon Foreigner, Rei is a mute ghost who died under mysterious circumstances and considers Midoriya her 'little brother'. Her real name is Morigawa Hitomi, and she was a test subject for the Noumu project before dying 30 years previously.
- Big Sister Instinct: She feels very protective towards Izuku, who she thinks of as her little brother. Unfortunately, there's not much she can do to protect him yet. It seems One For All is strengthening Midoriya's I See Dead People quirk, gradually making ghosts near him stronger to the point of being able to interact with people. She's eventually able to actively protect Midoriya by tackling Bakugou when he tried to attack him. She's also fond of Eri, who reminds her of Izuku when they first met.
- Black Eyes of Evil: Subverted. While she has something of an immature, cruel streak (though it is directed mostly towards those who are cruel to Izuku), she's still a fundamentally good person.
- Canon Foreigner: An original character developed for the sake of fleshing out Izuku's Quirk and giving him a friend.
- Creepy Child: She is physically and mentally a child who entertains herself with Body Horror and inflicts terror on people she dislikes.
- Creepy Good: As Izuku's friend, she helps him with whatever he needs, which usually includes helping other people.
- Dark and Troubled Past: A poltergeist who was an unwilling test subject for All For One's Noumu experiments, suffering horrific trauma at the hands of his scientists until she was rendered brain-dead. It's such that she doesn't want to remember her past, vastly preferring her new "life" instead as Rei.
- Death Amnesia: Doesn't remember how she died or even her name. She also doesn't want to remember, as in her opinion no one cared for Hitomi, she was killed, and no one cared. She only made friends and met Izuku as Rei, and prefers that.
- The Empath: Rei's Quirk.
- Expy: Rei is explicitly based on Erma.
- Ghost Amnesia: She doesn't remember being killed by All for One's Noumu experiments.
- Jerkass: Downplayed and justified. Dying as a child left her with a bit of an immature cruel streak, though it mostly comes out as pranks.
- Poltergeist: And unlike normal poltergeists who will typically revert to normal ghosts when they stop stressing out, Rei is like this permanently due to the intense trauma she suffered from being a test subject for Noumu experiments.
- Prophet Eyes: Averted. Being a poltergeist, Rei has Black Eyes of Evil.
- Satellite Character: Being dead, she doesn't have much to do except for following Izuku and helping him out.
- Suddenly Voiced: She speaks for the first time in chapter 39 when she rejects her human name. Izuku notes he's never heard her voice in the ten years he's known her.
- Television Portal: Like Sadako, Rei enjoys crawling through television screens. Unlike Sadako, there's no portal; she's just phasing through the screen. She can also travel through 3DS screens.
- Troubling Unchildlike Behavior: Justified, in that she's a ghost who was murdered through being used as a test subject for the Noumu project.
MikaA diluted calico and Izuku's pet cat.
- Cats Are Magic: Sort of, the ability to see ghosts is common to all cats in this universe, although not particularly magical. She does have a Quirk: she doesn't produce any allergens, making her perfect for Fuzz Therapy. She also seems to have an uncanny ability to be exactly where she is needed to perform Fuzz Therapy without Izuku knowing, from the Sports Festival to the Forest Training Camp.
- Evil-Detecting Dog: No contact with villains so far, but upon meeting Endeavor she throws an impressively loud hissy fit that gets him to leave Todoroki alone.
- Eye Scream: Suffered this at some point in the past, leaving her with only one eye.
- Fuzz Therapy: She is very good at providing this for Izuku and his friends.
- Little Stowaway: Sneaks her way into the training camp arc by hiding in Izuku's luggage.
- Mysterious Animal Senses: Like all cats in this world, she can see ghosts.
- Ridiculously Cute Critter
- Team Pet: Is slowly becoming this for Class 1-A.
- This Is My Human: A chat with Koda in a side story reveals that "My Person" is her name for Izuku in cat language, with other favorites including "Warm Person" (Shouto), "Nap Person" (Aizawa), "Float Person" (Uraraka), and "Quiet Person" (Rei). She's also protective enough to troll Bakugounote a bit by napping on his things, and is outright willing to bite Endeavournote if he shows his face around the dorms.
Bakugou KatsukiIzuku's former friend-turned-bully-turned-rival.
- But for Me, It Was Tuesday: Doesn't seem to recall the incident that traumatized Izuku enough to cause his first major bout of elective mutism. It's slightly ambiguous as to whether or not he didn't remember or was trying to bluff his way out of the confrontation; if the latter, it blew up in his face when Izuku folds it into his call out.
- Heel Realization: In a somewhat roundabout fashion. While watching Izuku's interactions with their kidnappers, Bakugou begins to suspect his bullying might have pushed Izuku past his limits and into a FaceHeel Turn. He's none too pleased by the thought that he could be responsible for that.
- It's All About Me: Very used to thinking that everything revolves around him. Such as his belief that Izuku specifically means to spite him with his actions. However, this is contributing to his gradual realization of the actual consequences of his behavior.
- Screw This, I'm Out of Here!: He immediately leaves the vicinity whenever the question of Izuku and Todoroki's relationship comes up.
Todoroki ShoutoIzuku's closest friend and queerplatonic partner.
- Asexuality: Todoroki is confirmed to be demisexual.
- The Confidant: Izuku comes to confide his worries and insecurities to Todoroki, who assures him and offers advice on various situations.
- Deuteragonist: After the Sports Festival, he upgrades to the main viewpoint character after Izuku.
- First-Name Basis: Eventually with Izuku.
- No Social Skills: He completely misses his classmates trying to skirt around outright asking if he and Izuku are sleeping together.Todoroki: Wait. What did you think we were doing?
Kaminari: Oh you sweet summer child.
- Platonic Life-Partners: He involves into this with Izuku. Both boys are asexual but develop a deep bond.
Togata MirioA third year and member of the "Big Three" at U.A., Mirio becomes Izuku's senior at Sir Nighteye's hero agency.
- Take Me Instead: She asks Mr. Compress to take her so long as he doesn't hurt Deku.
- Adaptational Villainy: Dr. Tsubasa is All For One's doctor and a Mad Doctor who converted his grandchild into a Noumu.
- Character Death: Dr. Tsubasa dies when he's unable to escape a Collapsing Lair. His ghost is then killed by the ghosts of the Noumus he created.
- Deader Than Dead: Dr. Tsubasa is not only killed, but then his ghost is torn apart by the vengeful ghosts of his many victims.
- Even Evil Has Standards: Dr. Tsubasa may be the Mad Doctor responsible for creating the Noumu, but even he is genuinely regretful over failing to identify the presence of Izuku's Quirk, years ago.
- Long-Lost Relative: Hino reveals that Dabi is a Todoroki.
- Mad Doctor: Dr. Tsubasa, All For One's doctor. He is directly involved in the creation of Noumu and even converted his grandchild into one.
- One Sided Rivalry: Toga views Todoroki as a romantic rival for Izuku after seeing their closeness at the Hero License Exam.
- Villain Respect: Mr. Compress is impressed by Eri's willingness to sacrifice herself to protect Izuku.
- Villain Takes an Interest: Shiragaki and All For One become interested in Izuku, even going so far as to have him kidnapped alongside Bakugo.
- Villainous Crush: Toga develops one on Izuku, even after he breaks he nose and knocks her out.
All Might's predecessor who died fighting the villain All for One, now she follows All Might around as a ghost and acts as a second mentor to Izuku.
- Affectionate Nickname: Calls Izuku "Sprout" and All Might "Toshi".
- Body Horror: How she looked when she died.
- Combat Pragmatist: Is implied to have fought this way in life, and is teaching Midoriya the same thing.
- Deadpan Snarker: Spends a lot of time keeping a running commentary on All Might's (mis)adventures.
- Dying Alone: When Midoriya asks Gran Torino if he was there when she died, he says no, nobody was.
- Friendly Ghost: She is a kind and friendly woman who mainly follows around her successor. She helps Midoriya learn hand-to-hand combat when she realizes he can see her.
- Jacob Marley Apparel: Zigzagged. She usually wears a tank top, but, as with all ghosts, she reverts to how she looked at death while under extreme emotional turmoil.
- Mentor Occupational Hazard: To All Might, before she even had the chance to be a mentor properly.
- My Greatest Failure: Nana sees her death like this since it led to her not being able to train All Might.
- Prophet Eyes: Comes with the territory of being dead.
- Satellite Character: Since her death left her unable to interact with the world meaningfully, she settled into following All Might around, at least until she met Izuku.
- So Proud of You: How she feels about All Might, and she regrets not being able to tell him so.
- Spirit Advisor: Though she tried to avoid doing this for Midoriya at first because Midoriya is All Might's student and she felt that it'd be unfair to All Might since she couldn't teach him herself. The attack on the USJ causes her to change this stance and start helping teach Midoriya to protect himself in combat.
- Undignified Death: Though it happened before the start of the story, Izuku sees the results.
- Big Brother Instinct: He wanted to protect his sister from Endeavor, but died in a car accident. He's grateful for all Izuku has done to save her.
- Everyone Has Standards: He won't Troll Endeavor when the man's on the job. He won't endanger people's lives just for his kicks.
- Jerk with a Heart of Gold: He hates Endeavor, but he won't do anything to his kids. Of course, they're also his sister's kids, so that helps.
- Mystical White Hair: His hair's natural color is white, just like his sister's.
- You Are Better Than You Think You Are: He gives one to Izuku, urging him to escape All for One's base when he's all but given up.
- Big Brother Instinct: He wants to thank Eraserhead because the hero saved his sister from his killer.
- Satellite Character: He rarely appears outside Eraserhead's orbit.
- Friendly Ghost: She's a Nice Girl who wants to do what she can to help Todoroki. Unfortunately, all she can do is tell Midoriya.
- Death of a Child: He was a very young when he was converted into a Noumu. He's no older than 15 when Stain kills his Noumu body.
One For All
The original holder of One For All and All For One's brother.
- Blinding Bangs: Has these like in the flashback image in the manga.
- Cain and Abel: The Abel to All For One's Cain.
- Friendly Ghost: He's a good man who helps Midoriya when he gets captured by All For One.
- Heroic Mime: Was a sickly child and between too many ear infections adding up plus getting the Quirk from All For One rendered him deaf.
- My Greatest Failure: Being unable to stop All For One.
- Only Known by Their Nickname: Much like All For One, he is only known by the name of his Quirk: One For All.
- Spirit Advisor: Being All For One's brother and hanging around him since his death, One For All is intimately knowledgeable of All For One and how he operates.