Bakugou Katsuki was 3 years, 8 months, and 27 days old when he went missing.

At first, his parents had simply assumed that their son was out playing with his friends, but as evening fell and the sky grew darker and darker, worry began to sink in like a cold stone in their chests. Katsuki had never come home this late, and it was getting dark enough that he might have trouble finding his way.

"I swear, I'm going to drag that little brat home by the ear and make him pay for making us worry over nothing. Does he even realize the effect his actions have on other people?" the mother ranted as she pulled on her shoes.
"I know, I know, I'm scared too, but I'm sure everything will be alright. We'll find him soon, okay?"

Bakugou Katsuki was not, in fact, found soon. The Bakugous' search that night proved fruitless, as did the subsequent police investigation. They kept the case open for as long as they could, despite having no success and no leads. It was not for a lack of investigation or effort that no leads could be found. Bakugou Mitsuki was a woman one didn't cross if one valued one's life, especially not when something as important as her son was on the line. And it was not simply fear of the woman's wrath that had people devoted to the case. It was easy to sympathize with the grieving family, difficult to watch their desperate hope fade with each passing day. However, it was all to no avail. Indeed, it was as if Bakugou Katsuki had simply vanished into thin air.

Bakugou Katsuki was 3 years, 8 months, and 27 days old when he developed his quirk.

He had always been sure he would be an early bloomer. He was destined to be number one in all things, after all. First in the class, number one pro hero, top of the food chain. It was only logical that he'd develop his quirk early, that he'd develop a strong and powerful quirk. He was destined for greatness, and soon enough, he would have the quirk to prove it. It would come any day now, he was sure of it.

Indeed, Bakugou Katsuki was more right than he knew. For at that very moment, deep within him, something started to shift, to change, to bloom.

On the other hand, his thoughts continued, the crybaby Deku trying to catch up behind him? Definitely going to be a late bloomer. Hell, what with how useless he was, he might even turn out quirkless!

Midoriya Izuku would, indeed, not bloom at all, but that is neither here nor there. For now, he was simply trying to catch up with his friend, who had shot off ahead and left him behind once more.

Soon after his friend had turned the corner, Midoriya Izuku rounded it only to find the other boy nowhere in sight. He hadn't been that far behind. Certainly not long enough for the other boy to have run far ahead or to have turned down a side street. There weren't even any alleys here to hide in, though that was a moot point, given that they both knew better than to go into them. Despite the seeming impossibility of it, the facts remained, sharp and ugly in the dim light. Midoriya Izuku had been left behind once more. He turned to head for home dejectedly, a "Stupid Kacchan" escaping his lips as he kicked a can down the street.

Bakugou Katsuki was 3 years, 8 months, and 27 days old when his body faded from existence.

As he ran, he started to realize that he was feeling lighter than he should. Not in mind, but in body. He looked down at himself, stumbling to a halt. His arms were more transparent than they should be, and were steadily growing more see-through. The thought hit him. Could this be his quirk coming in? Of course it was, he thought to himself a moment later. What else could it be? So, what was this? An invisibility quirk? Or perhaps intangibility, judging by how little weight he seemed to have. Not quite as flashy as he might have hoped, but definitely powerful. He could work with this. He could definitely work with this.

He was snapped from his musings about his new quirk by the realization of how his thoughts were becoming more sluggish, how thinking was becoming more of a struggle. Something was wrong. Something was very wrong. He had to reverse what was happening. The only problem was that he had no idea how he had triggered his quirk, much less how to reverse it. Breath coming in short, sharp bursts, he concentrated with all his might, a might that was diminishing with each passing second, on undoing what was happening, of going back to visibility. Despite his best efforts, he only grew more transparent, and, he realized in horror as he studied himself more carefully, bits of his form, bits of himself were evaporating off of him like swirls of steam.

In that moment, whatever pride might still have been holding him back vanished in favor of sheer survival instinct. With what words he could still string together in his mind, he begged, he pleaded, he-

And then Bakugou Katsuki knew no more.

Bakugou Katsuki was 3 years, 8 months, and 28 days old when he woke up in a body that was not his own.