It didn't take a genius to realize that Nox had been coming home earlier than usual and Izumi had to wonder if it was because Nox thought he was going to try to... try something again or rather he just normally had less work to do at this time of year. He never was able to bring up enough courage to directly ask, although he did occasionally hint at the question and try and drag an answer from the older. It was as impossible as drawing blood from a rock, but it was good practice for prying so he kept at it anyway.
Summer slowly grew closer and closer and Izumi was already registered for his next semester of classes- he'd impressed everyone surpassing their expectations and testing into the second semester of several grades ahead of where his age group should be, and three semesters ahead of where they had predicted he would be and spent two whole days glowing (more like blushing and stammering profusely) under their heavy praise. Nox had given him a flash of what almost looked proud smile and a 'impressive, nicely done'.
Izumi only realized by the time he went to bed that he had excitedly spoken about it for over half the night. And so Izumi spent most of the night worrying about that and fretting over how to apologize. By morning he felt miserable.
He shouldn't have gotten so caught up in it, it was just school, he must have been boring Nox too- how could he have not noticed how rude he was being if he really was that smart? Maybe he should ask to remain on his current course. He didn't have school that day but by the time he had woken up and dragged himself to the kitchen itching with shame he saw that the other had made him katsudon for breakfast with a note declaring it was for him too. The small gesture had him relaxing. So for once he hadn't messed up then. Probably.
That evening Nox had returned even earlier than usual- not a trace of accusation or anything but fond pride on his nearly blank face- and pulled from the refrigerator a homemade cake that read, in careful iced words, 'Congratulations.' Izumi was never quite sure how or where it had been hidden because he knew that he hadn't seen it, but he ended up spending the whole of the next day unable to contain the smile that had formed.
Maybe, just maybe, Nox was a little bit proud of him.
Probably not, it was just grades after all, but Izuku couldn't help but dream that he was. All the same he still found himself wondering why exactly Nox's schedule was changing.
Nox never took weekends off from his job, but Sunday he had always gotten off before lunch and this hadn't changed in the months Izumi had been living with him, so fifteen minutes before noon he was unsurprised to hear the quiet click of the door. He'd just gotten back from the market again where he'd spent the morning getting the food needed for the next three day's meals- he made a point to leave the house every three days for small trips of food and again whenever necessary for any other supplies to make sure he still talked with other people.
"Izumi?"
Startled, Izumi jumped slightly from his meandering thoughts, "Huh?"
"Right then, clearly you need to get out and enjoy the fresh air." Nox gently pushed him to the side and efficiently finished unpacking the last of the groceries to Izumi's stuttered protests.
"Wh- hu- n-no- I've go this! Don't worry about me I-I'm fine, really!"
"Look at you, you're paler than paper, you can be as good at analysis as you like, but you still should make an effort to stay in shape and healthy." Nox clucked disprovingly as they ushered him out the door. Outside the front door were three more doors, two locked on either side of the square hallway and one directly across. As usual Izumi headed towards this third one and together the two went down the stairwell which led- after opening another door- to the outside. Nox lived in a remote place near a remote village in a difficult to spot house. Izumi had at one point made it a game to spot where the house was located, but had given it up after only an hour as a lost cause when he couldn't find a single sign of it.
He trailed along after Nox as they stepped outside and shortly after Nox picked up his pace into a sort of trot expertly guiding through the trees as if following an invisible trail. A few minutes later when Izumi was more than slightly out of breath the pace picked up once more and they were truly running, Nox with an almost un-human type of grace and Izumi simply struggling to keep up. Nox leapt over logs bounced between rocks and lunged off of tree limbs with a constant, smooth pace that would leave even professionals jealous while Izumi panted, sprinting as hard as he could in a desperate effort to just keep up with the other.
He had to wonder how much practice the other had and if Nox even knew the answer himself. He frowned thinking back at the occasional comments, the careful deflections about age and childhood hobbies, the occasional way his brow would furrow at points, fingers tapping, it was the little things that gave Nox away mostly, the opinions so wildly belonging to a different time, his knowledge of false identities, knowledge or lack of knowledge he shouldn't have. He had some form of memory loss, that Izumi was near sure of, and he was almost definitely far older than he looked.
"Almost there!" It wasn't even fair how level his voice was, as if Nox had just been touring about a museum in search of his favorite work not jumping through the woods.
"W-where." This time the stutter wasn't from nervousness or even habit, just from sheer breathlessness.
The pace slowed some and soon it was almost a jog again, "You'll see."
They made a small loop around Izumi wasn't sure what and then Nox turned, their pace having slowed almost to a walk again, and Izumi gasped at the sight before him. The area they had made a wide loop around was apparently a large clearing with a lake of pure water sparkling in the sun, so clear you could see the bottom, and bright wildflowers thickly coating the ground. The trees offered some shade on half of the clearing spreading a fooled light all over.
Izumi couldn't help but stare in awe, "wow..."
Nox only smiled slightly, and as briefly as always.
The runs became a normal thing from then on, sometimes going longer, sometimes shorter, but always ending in the same clearing and slowly bit by bit Izumi stopped struggling as much to keep up with the other as they soared through the forest with the ease and skill to make even the animals who lived in it jealous. The summer and the following autumn flew by easily and in no time Izumi was nearing the end of his online school curriculum as he also worked through the self defense lessons Nox had added on at the end of the run before they entered the clearing. Like anything else Nox did, the lessons were far from typical, and instead of learning just to use himself to quickly knock out opponents or how to dodge, he also learned to use his surroundings and to think on his feet. Nox had no qualms with fighting dirty it seemed, even unknowingly encouraging it. (Actually, he seemed to think of it as an attached part of it 'Well, I should hope if you're stabbing someone in general they're not your ally so good..?')
All the same Izumi was finding himself increasingly curious about what Nox's job was as time grew on, it almost seemed like he was a jack of all trades at times which really made Izumi wonder what exactly required such a vast extent of skills.
Nox could fight with the best of them. He was in shape. He could cook very well. Read micro expressions. He had a fair amount of medical knowledge. Mathematical knowledge. He knew English, German, Chinese, Japanese, Latin, Greek, and an assortment of other languages fluently. He knew how to disguise himself. How to fish. How to drive. How to cheat at cards (and Izumi only knew because Nox offered to teach him). At a coin toss. At a dice roll. How to cheat at picking a number games. He could sing. Knit. Sew. Shoot. Clean. In fact, Izumi was beginning to struggle to find things he wasn't good at rather than ones he was; he had found two.
Nox couldn't figure out technology and was so far behind with only an old laptop computer and a even older radio (which you charged by winding it up) that when Izumi first realized how hopelessly behind with it Nox was he thought they were joking. They were not. The second thing was current events, he seemed to try to read the news, but no matter what he was always several weeks behind. It was as if he was stuck in the past. Or rather as if he was trying to go back to it.
More and more Izumi found that conclusion made sense, the constant insistence that quirks were around far longer than scientists guessed, the old cookbook-which Izuku quickly found out one of the handwritings was actually Nox's-, and a ton of other proof all pointed that Nox was much older than he looked. The final proof was after two years of staying there when Izumi glanced over and came to the sudden realization: Nox had not aged a single day from when he first saw him. He was more open and friendly with Izuku, but he had not changed in any other way. It made him see the old photograph he had found in the other's room- an essentially empty place with only a chest of drawers filled with black clothes and a bed- when cleaning it in an entirely different light.
The photo was older than old and of two people one that looked like Nox, but with messy, light brown hair and pale green eyes. And smiling, wide and openly. Both people wore old styled clothes as if it really was from the time before quirks, but on his face with the uncharacteristic wide smile, contentedness shone in his eyes. At the Nox-look-alike's side was a woman than looked, around Nox's age; just freshly out of her teens, perhaps even late twenties. She was beautiful, with carefully braided dark hair and a shade of eyes almost identical to his own. A few freckles dotted her cheeks and a smile graced her face that could be only described as angelic as she hugged the look alike tightly while gazing at the camera as well.
At first Izumi had thought it was a photo of a great, great grandparent or maybe even a great great great grandparent- it was definitely old enough for any one of those options- but the more he thought about it the more it seemed less likely. And with nothing else to think about he began to think about the mystery of Nox more and more often.