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The Shinigami World is a separate plane of reality that overlooks several worlds. The Shinigami can observe and steal life from many different worlds. However, they are only allowed to drop their notebooks or visit certain places. The Shinigami king doesn’t trust the quirks of the hero aceadmeia world and has forbidden anyone to visit that world on punishment of death.
Grelus is a Shinigami who likes to people watch. Over the years he’s watched a lot of different people. His current favorite person is Inko Midoriya. He watched her grow up, get married, and have her son. When Izuku is still in grade school, she and Izuku are attacked by a villain and Grelus saves them by killing the villain. Shinigami aren’t allowed to use their powers to save people and Grelus dies. Grelus was Rem’s best friend so she decides to go protect Inko. Fortunately Izuku is quirkless and she comes up with a plan.
Rem makes a deal with the Shinigami king. She will go to the hero world as long as nobody finds out the truth of origins. If anyone suspects that she is really a Shinigami from a parallel dimension, the king will kill her immediately. As long as she can pass herself off as a quirk and follow all the other death note rules as well, she can stay. (Suicidal thoughts warning because it quickly becomes obvious that Rem has no intention of returning to the Shinigami realm.)
Rem flies down to Izuku’s room that night and sets Grelus’ death note on Izuku while he’s asleep, thus giving him ownership. While he’s still asleep she rips one corner of a page out and goes to Inko’s room. She touches Inko with the death note scrap while she is sleeping. Izuku wakes up, notices the notebook and then Rem. He’s not afraid of her, just excited. Even more excited when she tells him she is his quirk. She shushes him and explains how ‘the quirk works’ before letting him tell Inko. She says that notebooks are his favorite possessions so the anchor that connects Izuku and Rem is that black notebook. Izuku must never write in it and must never let anyone else get their hands on it. (Death Note cannon is unclear on this point. But if possible, Izuku should loan his notebook to Rem and let her carry it. However, the ability of Shinigami to interact with physical items isn’t thoroughly explored and I make several assumptions for this fiction) If Rem can’t hold onto the notebook for Izuku, she convinces him to hide it. Rem doesn’t tell Izuku the extent of her abilities.
Inko comes to wake Izuku up for the morning and is understandably freaked out. Rem explains that she is Izuku’s quirk, here to protect him after the traumatizing event yesterday. Quirk manifestation because he was in danger for the first time. Inko calms down quickly and takes Izuku to the doctor a.s.a.p.
Rem doesn’t tell them she is invisible, lets them find out when nobody else can see her. Just says she doesn’t trust anyone else. At the quirk specialist, Rem sits passively and refuses to participate in most tests. Izuku eventually convinces her to pick up a few items to prove her existence. She pretends for the doctors that she can’t hear or see anything that Izuku doesn’t already know. The doctors try to show Rem cards and have Izuku tell them what they are, things like that. Rem wants to keep Izuku off anyone’s radar. She knows sentient quirks are rare so she pretends she isn’t able to see anything he can’t.
The doctors let Izuku call his quirk Invisible Friend but make notes that Rem is probably psychosis or a product of Izuku’s subconscious. Created by a traumatic event and his loneliness. She’s kind of his opposite; female to male, cautious vs friendly, unhelpful vs eager to please. Izuku might just have telekinesis like his mom and Rem is his imaginary friend.
At school the teachers don’t have an excuse to ignore Izuku anymore. Bakugou still doesn’t get in trouble but Izuku isn’t picked on by the entire student body. Partially because Rem fights dirty. She doesn’t start fights but retaliates against bullies. Bakugou gets his things stollen, homework ruined, tripped, pushed, shoe laces tied together, tacks on his chair, and pins in his shoes. Izuku has an ‘invisible bitch’ protecting him who refuses to fight Bakugou beyond giving him a shove or a smack. Rem starts carrying around needles to use on bullies. And this is how Mrs. Midoriya and Mrs. Bakugou got called to the hospital to pick up their sons for burns and Katsuki having broken sewing needles stuck under his skin the school nurse couldn’t get out.
Grelus loved Inko not Izuku so Rem tells Inko she will do everything she can to stop Izuku from being a hero if that is what Inko wants. Inko tells Rem to help Izuku.
Izuku starts ‘quirk training’ with Rem. She can only be 100 meters away from him (Vol 13 of Death Note says the Shinigami has to stay close to the human. In episode 9 of the anime Ryuk claimed he circled Light at 100 meter radius) and can only interact with or carry so many objects before she gets tired. She can also take very small objects and ‘hide it in her wings’ as Izuku calls it, which makes the item disappear. The spines on her shoulders are a pocket/her folded wings that she can hold things in. This is where she keeps her own death note and pen, not that she tells Izuku this. She can only hold human items this way for a little while before she turns intangible and whatever she is holding falls out of her pocket. If she gets too tired she falls asleep and has to take at least a quick nap before waking up. Rem denies that she actually sleeps, just rests. Sleeping is lazy. At night she reads or listens to music while Izuku sleeps. Izuku gets Rem to lift weights and try to improve. Rem knows that the other Shinigami are laughing at her but she’s not planning on returning so she doesn’t care. She never tells him she has the ability to kill people or what would happen if he wrote in his notebook, just that he has to touch it once per year or Rem will disappear.
Izuku can feel a pull in Rem’s direction when she nears the edge of her range (or thinks he can). This probably wouldn’t happen with normal Death Note but Izuku is a smart kid who thinks his quirk would work that way, mind over matter.
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Rem does research into quirks. If she can find an excuse to ‘evolve’ then she can give Izuku the Shinigami eyes or tell him she can kill people.
Things for Izuku and Rem to work on, stealth, Pressure points, hand to hand where Rem boosts Izuku. Observation telephone, where Rem describes something she sees and Izuku analysis it, weight lifting for Rem, maneuverability and parkor so Izuku can stay in range if Rem flies away.
As a Shinigami Rem is able to understand all human languages. She probably doesn’t tell Izuku this and just claims that she studies other languages at night while he’s asleep. Her previous birds eye view of the world would also have given her access to certain classified information that she can tell Izuku or she can give him hints to figure out himself as she sees fit. Rem has poor handwriting in Japanese but she’s able to write or touch buttons. Meaning she can leave notes or send text messages without Izuku’s help.
Izuku is able to go to gyms and enroll in self-defense classes now that he has a quirk. They wouldn’t take him earlier because of ‘liability’ and ‘safety’ concerns. Rem had an eye in the sky view of the world until recently so she knows that the hero system is corrupt. The Shinigami world can see anywhere on the planet so she learned a lot about the world. With her encouragement/nagging Izuku is mostly convinced to go underground rather than daylight hero.
Izuku’s muttering is more pronounced than in cannon because it is how he talks to Rem and because it is part of his quirk, the other students and teachers can ask him to stop but don’t be as mean about it.
Okay side note here. I feel Bakugou should have received more consequences for his actions. Yes, he’s a better person now but he got away with years of bulling and suicide bating with basically zero consequences. While true to life, I prefer more satisfactory comeuppance in my fiction. However, if Katsuki hits his friend because his Mom hits him at home, his actions become far more forgivable. I also like the fan theories that his nitroglycerin based quirk is a mild toxin effecting his moods or brain chemistry. Basically, I want him to have a justification for his behavior. Maybe he’s acting out because he doesn’t know what a healthy relationship looks like or he has an undiagnosed quirk illness or mood disorder.
Bakugou and Izuku have a better relationship than in cannon. Rem has no scruples about telling Inko about Bakugou’s bad behavior so Inko is very aware of everything he does. If Rem sees Mrs Bakugou hit Katsuki she will absolutely tell Inko, convince Izuku to tell the teachers, or send in a report herself. Rem would also do research and suggest to Inko that Bakugou needs anger management and counseling.
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If Izuku encounters the sludge villain, Rem is able to stab him in the eyes repeatably until he lets go of Izuku. Izuku won’t need to ask All Might any questions.
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For the entrance exam, Rem stops Izuku from tripping on the way in. When Iida calls out Izuku for muttering Bakugou takes offense. “Hey! Muttering is part of his quirk, asshole!” Friends or not.
At the doors to the practical entrance exam, Izuku stands close to the doors while Rem flies off to scout. When the test starts she directs him to where the robots are. She rips wires out of the wires of one bot before Izuku realized the robots have an off switch. He has Rem fly alone to deserted parts of the map and turn off as many as possible. Ripping wires out is tiring but she can flip a lot of switches without getting exhausted. Rem flies back to check on Izuku when the zero pointer arrives. Izuku goes to try and help Ochaco and tells Rem to try and find a way to disarm it. Rem disconnects a few wires and the teachers shut it down.
Rem is exhausted and needs to sit down and go to sleep. Izuku can’t move far from where Rem is sleeping. He stays with Ochaco and explains how his quirk works while Rem naps.
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Fitness tests on the first day. Rem can give Izuku a push for most tests to help his performance. For the ball throw Izuku asks what the score will count as if he makes the ball disappear. Aizawa tells him not to slack off and if he can make it disappear, do so. Izuku stands on his toes to hold the ball near Rem’s shoulder so he doesn’t have to lift it as far. She puts it in the spines on her shoulder and it disappears. Aizawa tries his quirk on Rem and she turns intangible, making the ball reappear. She can feel his eyes. She either purposefully becomes intangible to make herself look like a quirk or his quirk really does effect her sightly. Hakagure is last place canonically.
Izuku’s classmates ask about Rem. He brings one of his old notebooks to class to show them sketches he drew of her. They are surprised by how scary she looks. Rem refuses to be friendly or indulge any questions. Again, she insists that she doesn’t trust anyone and won’t let them see her.
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Izuku’s hero outfit is designed for reconnaissance and stealth. He has technology and weapons that are small and light enough for Rem to use. Trackers, cameras, needles, wire, darts, ect. He also has an earpiece that he can give to her so they can talk long distance.
Rem disagrees with All Might’s lesson plan. She uses the communication device that is part of Izuku’s outfit to text other teachers, whatever numbers are preprogramed into the device and complain. Izuku says “Rem, No! It’s All Might!” Bakugou: “OMFG, Nerd, learn to control your quirk. Yeah, he does this all the damn time.” The exercise continues as planned but only after All Might reminds everyone that this is the first class so light sparing only, you are working on teamwork and stealth. Rem is of course, prefect for this assignment and with her help Izuku’s team dominates.
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Rem can’t be seen by anybody so she’s not much help at USJ. Izuku might tell her to leave him and go help Aizawa in the courtyard but she wouldn’t listen to him. Her priority is Izuku’s safety. If she does fight Tomura and Kurogiri then they would both be very confused by some invisible person pushing them. If Izuku thought of this before, Rem might grab a few hairs from each of them. DNA test can be run on any evidence Rem grabs. This would reveal Kurogiri’s identity earlier than in canon.
To Shinigami eyes, the Nomu names look like a jumble of different names. Or like mirage names going in and out of focus. If you stare at it long enough you can pick out bits and pieces.
After USJ, Rem decides Aizawa would die to protect Izuku and is therefore trustworthy. Izuku asks her to check on Aizawa’s condition so she spies on him while he’s in the hospital. When nobody is looking she also steals a scrap of Izuku’s notebook and touches sleeping Aizawa with it.
When Aizawa returns to class he can see Rem. Bit of a surprise for him. Rem says nothing beyond that she trusts Aizawa now. When the other teachers realize this and pester Aizawa about it, he will confirm that yes, Rem really does look like Izuku’s sketches.
Sports festival round one would go almost exactly the same. Except, Izuku’s stunt with the mines isn’t nearly as risky. He has a plan to land, Rem stands where he is about to land and catches him just enough to slow his decent.
Round two, Izuku teams with Ochaco. If Ochaco makes everyone weightless, Rem can pull them anywhere through the air. Their team has the power of flight.
The one on one matches would be reliant on Izuku’s fighting ability. Rem could trip or push people but not much else.
I don’t know what internship offers Izuku would get. Rem as a quirk is very good for search and rescue. Rescue heroes like the Pussy Cats might be interested.
Shinigami eyes become relevant to the plot after the sports festival when Rem realizes Iida only has a few days left to live. Rem doesn’t care beyond that Izuku would be upset. In the past she has asked Izuku about why humans do things and to explain human emotions. She asks why Iida says he’s okay when he isn’t and why he doesn’t go home to be with his family. If something happens to him does Izuku understand that he did everything he could?
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Rem has no patience for Mineta. I have mental image of him discovering the hole in the locker room wall, only for Rem to pick him up and carry him to Aizawa.
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While shopping for camp, Tomura corners Izuku. Rem leaves to get help at Izuku’s insistence. They have a secret code to communicate mid-conversation or non-verbally. That’s exactly the kind of thing Izuku would invent.
Rem finds Ochaco and stealth tags her with the Death Note scrap. Ochaco is of course surprised and has a minor freak out. Rem doesn’t have time to be nice. She makes her call Aizawa immediately. If Aizawa can hear Rem over the phone (Death Note canon is unclear if Shinigami appear over camera to people who can see them) she explains the situation. If he can’t hear Rem, she bullies Ochaco into repeating what she says word for word. Rem shows Ochaco where to spy on Tomura and Izuku without being seen, probably from the second story. Rem then flies back to Izuku’s side. Aizawa, of course, has to yell at Ochaco to stay where she is and not get involved. Tomura eventually leaves Izuku and Rem follows him as far as she can. He’s probably picked up by Kurogiri outside the mall.
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I have no idea what Ragdoll’s Search ability would sense from Izuku and Rem. That might lead to some interesting conversations. Of course, Izuku is clueless as to Rem’s real identity.
Rem would treat Koda as one of Izuku’s bullies and he would have to ask her to please be nice to the traumatized kid.
For ‘quirk training’ Rem needs to work on her strength more. If she gets strong enough, she could theoretically pick up Izuku and fly him around.
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As a gift, one of Izuku’s friends commissions artwork of Rem based on Izuku’s sketches of her.