I'm new to writing but this is the first part of a story that's been in my mind for a while now. This doesn't get to the first part of the anime/manga but does hit a key part of Shoto's Backstory (so its more angsty than the rest of the story would be) Fair warning the rest of the intro will also be kinda angsty just cause my OC is a Todoroki and and that means their childhood was gonna be rough. But once they get to UA it will be much less so, it's meant to be a romance after all.

I'm gonna leave it for a few days and see what happens, if it seems like anyone wants my to keep going I'll add the next chapter after that and it will soon be on to the key events in the timeline.

Also, I made up what their grandparents quirks were to have it make sense what OC's quirk is and where it came from, rn they are pretty weak, but keep in mind they are 5, so the description is more so for teenage OC, at the moment they are just a little kid who has only had it for like a year. I wanted them to have a quirk good enough to not always feel inferior to Shoto (and so Bakugo respects them) but not so good that they will automatically beat anyone they fight.

Appearance: Shares most of her features with her mother Rei (Snow white hair and very pale skin), however her eyes are a mix of blue and grey (heterochromia like her twin but not one of each, they are grey with streaks of blue)

Quirk: Sound Wave - Mix of Rei's mother's quirk Sound Manipulation and Enji's mother's quirk Pressure allows her to emit pressurized sounds waves from her body (primarily hands), muffle or amplify noises around her, and (through a lot of harsh training by Endeavor) "echolocation" using sound waves through both air and solid objects

Name: Hibiki Todoroki (written with the Kanji 響 meaning echo, named for her strong resemblance to her mother Rei)

5 Years Old:

Hibiki woke in a cold sweat. She wasn't sure what was going on and reached out on instinct for her twin Shoto for reassurance. When she found no-one beside her she panicked for a moment before she remembered that her other half no longer slept in the same room as her. Oka-san had strongly objected to separating them but Oto-san had insisted that he had to abandon all distractions to train to succeed him once he had developed his dual quirk. He thought that Hibiki's quirk, while also a mix of his and Rei's mothers, was not strong enough to be worthy of training. Hibiki had cried for weeks after being separated from her onii-san, Oka-san had attempted to console her but even as a child Hibiki could see how her mother was strained. She hadn't told her but ever since her quirk had shown up she was able to hear her Oka-san sobbing in her bedroom when she was alone.

Hibiki once again began to quietly sob as she thought about the state of her family. One thing she had learned to do without training with her quirk was muffle her sounds, between not wanting her Oka-san to be sad when she heard her crying and not wanting to draw her Oto-san's attention (and wrath) she had already become skilled at doing most things in near complete silence. After she had cried herself out, between the tears and the sweat that had now dried she was thirsty. She slid out of her bed and shivered when her feet hit the cold floor, even with her beloved Oka-san and (now half of) Onii-san radiating cold she still wasn't used to it. She padded silently down the winding halls of her family's massive traditional Japanese home toward the kitchen, intending on finding a late night drink.

A few halls away from her goal Hibiki stopped as she heard a sound that chilled her to the bone, her brother's scream of pain. She had been kept away from her other half for the most part since their Oto-san had forcefully separated them, but for a few secret meetings. Even without being physically close both the twins strongly relied on their connection to know the other was ok, strongly believing if the other was ever truly hurt or in danger they would now. Hibiki clutched her heart as the sounds of her onii-san's pain echoed through their lonely house. She immediately began sprinting in that direction as tears filled her eyes, desperate to reach the person she loved most in the world and save him somehow from the pain.

She turned the corner to the kitchen as the sight before her was terrible, her mother was standing over her injured, crying twin, and did not kneel to help or console him, despite the tears in her own eyes. Her Onii-san, who was clutching at the left side of his face, kept wailing and screaming. Through his fingers Hibiki could see the beginnings of a terrible burn and she wondered why her mother wasn't helping him. She screamed as she ran towards her twin "Shoto-nii! Oka-san!" and reached out to her twin with tears in her eyes.

He looked up at her and the eye she could see widened in what looked like fear. As Hibiki was running towards her other half with her hands outstretched she watched in disbelief as he took his left hand off of his face and sent his fire towards her, screaming to stay away. The sight of the fire seemed to rouse her Oka-san from her trace who moved quickly to grab her female shield and try to save her from the flames. Hibiki screamed as she felt the fire burn her hands, while not as bad as the burns her twin had sustained it was the first significant physical pain she had felt in her life and it destroyed her that it came from her beloved twin. So distraught she didn't initially notice that her long white hair, so like her mothers, was also smoldering until her mother, using her ice for the first time in front of the twins, froze her hair to prevent it from fully catching flame.

This was the situation Endeavor found when he barrelled into the kitchen moments later, having been in his office on the other end of the house when he heard Shoto begin screaming. He found his heir, nearly catatonic on the ground with a horrific burn on his face, staring in horror at his twin who was half screaming half sobbing not sure what to do with her burned hands. He also noticed what Hibiki had missed when she saw her mother standing over her twin, the discarded teapot on the ground near his son. Between that and the fact that his wife was brokenly crying next to her children he could tell what had happened. He quickly moved to call the authorities before restraining her so she couldn't hurt either of her children again.

The next couple of hours were chaotic. Endeavor was relieved to know the Hibiki's burns were relatively minor and should heal with minimal scarring but was surprised to learn that hers were from contact with a flame rather than boiling water, as Shoto's far more serious facial burns were. As he brought the twins back to their home, without their mother who had made sure would reside permanently in the hospital as she had proved a danger and distraction to his heir. He observed his twins as they rode home in the town car, normally when they were together they would have to be pried apart, but now Hibiki was cowering in the corner of one seat with her bandaged hands tucked into her chest, seemingly trying to be as far away from her brother as possible. Shoto also seemed to be in shock, staring blankly down at his feet, the only time he showed interest was when Hbiki shifted. His one exposed eye, the other heavily bandaged, would flicker to her and she would curl in on herself further and Shoto would flinch to himself and then avert his gaze again.

From their interactions Endeavor could infer that it was Shoto's flames that burnt his twin and that neither had really processed it yet. His eyes narrowed as he contemplated if this would further affect his heir's training and decided to give them some time but that if he found it did he would have to step in and force them to resolve it.

Two Days Later:

Hibiki thought her life was painful before, she could have never guessed that it was going to get worse. Even without her twin (she flinched even now just thinking about him, she couldn't process how he could ever hurt her) she had still had her Oka-san to care for her. Now it was a maid that she wasn't very familiar with that would feed and dress her and "supervise" her as she played, really she only saw her when Endeavor checked in that she was being cared for. That was another unwelcome change, she now seemed to have a lot more of her Oto-san's attention than she ever wanted. The only supposed upside was now she and Shoto had a designated time they could spend together, but even now that was scary and sad, as she hadn't really processed what happened and whenever he looked at her it felt like the burns on her hands throbbed harder. So their time spent "together" was mostly her avoiding looking at him as much as possible, sitting quietly and waiting for it to be over so she could flee. Neither of them talked after the first day when they both ended up sobbing.

For now Hibiki tried to make the best of it, such as taking advantage of her unsupervised playtime to explore outside. Her hands still hurt too much to hold toys or draw, so she settled for walking around the garden in the back of the house until she was forced to sit with her brother for an hour. She was sitting crossed-legged by the koi pond with her hand hovering over it contemplating how best to play with them one when a voice behind her startled her.

"You'd be better off not sticking your hand in there little girl, don't want your bandages to get wet"

Hibiki turned and saw a man she wasn't familiar with standing in her family's garden behind her, to her five year old self he was giant, but other than that nothing was particularly interesting about his appearance, besides that fact that Hibiki hadn't noticed him coming up behind her. It was rare now with her quirk that she didn't know when someone was approaching her.

"Who are you mister?" she asked him curiously.

Usually if her father had people over for business he specifically avoided his children, calling them distractions, so it was rare for her to encounter an adult who didn't work for her family. The man chose not to answer, instead coming closer to her and as he did she noticed his smile become more menacing. Despite being a child Hibiki did still have some instincts, and all of her undeveloped gut was screaming at her that this man was not nice and she should go find an adult, or even her Oto-san. She knew that she'd never be able to outrun him so she opened her mouth, ready to use her quirk to let the whole estate know her distress when the man moved faster than she could follow and she felt something hit her head, sending her into cold, unfamiliar darkness.

Thank you for reading this far! LMK if you want me to post the rest! (sorry its a cliffhanger, it seemed like it was getting long, not all chapters will end like this)