Akira Agarkar Yamada is 15 and has never shot and killed anyone.
Akira Agarkar Yamada is 25 and almost shoots and kills an alien.
Akira Agarkar Yamada is still 25 and is unfamiliar with guilt like this.
Akira knows the Bermuda Syndrome firsthand. He can vaguely remember a youth of moderate wealth, but his clearest memory is blinking awake on his father's lavish yacht, thousands of miles out from where they began. And of being alone on that boat, living off of whatever had been in the galley until DUCK found him. He was 15 years old, then. He didn't know his own name, didn't know how he got there. It takes him 3 years to remember it; his name, his life Before, and by then he's already an agent, already too entrenched in the organization to go back. His name was never Akira, but that's the one he chose before he remembered, and it's the one he keeps.
After DUCK found him and discovered he had no memories, they recruited him. He swallows the story about aliens easily, because he has no other explanation for his circumstance, and because it makes sense, in an odd way. So he accepts, because there's nothing else in the world for him anymore, nothing else for a boy with nothing in his head besides an empty boat. He does his job, he goes undercover and to his mild surprise, there are aliens he meets, and convinces to go back to where they came from. They don't usually bolt or try to hurt him, and no alien exerts the same strange power of the thing in the ocean. He doesn't care, though, about any of it until he remembers Before.
It comes in bits and pieces, at first. He remembers he has a little brother, and his chest hurts. He turns 18 and dreams about his mother. Eventually he can remember more and more and then the bigger picture paints itself in full, and the last thing to come is his name. But he no longer has the capacity to feel sad for any of it, so he keeps calling himself Akira. He gets angry, sometimes, because he can't go back, and in part is angry because he isn't sad, because he can't be sad anymore.
So he storms into Headquarters after everything returns to him and demands to be told the truth, entirely and in full. George Ace smiles and takes him into the room where the leaders meet and shows him what DUCK is really for. It's the first time he ever hears the phrase "Bermuda Syndrome". He's promoted on the spot for "showing enthusiasm for the cause" and allowed to work on The Real Case.
He gets his duck later that week, and names her Tapioca. He takes her everywhere with him, even on investigations, and loves her like most people love their dogs. The anger subdues itself over time. Having Tapioca helps greatly, and it makes him feel a bit silly that the happiest thing in his life is being overly indulgent to his pet duck. And anyways, she stops being his pet and becomes his friend after about a year. But the determination to stop whatever is causing the Bermuda Syndrome remains.
Akira Agarkar Yamada is 21 when he discovers that to date, he is the only person who's long-term memory has been affected by the Bermuda Syndrome. And that's when everything changes.