Ao no Hako is honestly one of the best fits for a one-shot of any I've read. It's that kind of sweet, pure romance that would risk becoming stale in a serialised story. It's nothing too complex, but that's to its benefit considering the format, and it's well aware of genre conventions and when it's best to abandon or lean into them. It's surprisingly funny, but not so funny that it takes away from the sincerity of the characters' emotions (and, boy, these characters are nothing if not sincere), and it all feels about as natural as manga really can.
I really don't think I could ask for much more. This is one of the best one-shots out there. I'd highly recommend it as a quick pick-me-up.
Just as an aside, though: I also appreciate that the story focuses as much as it does on the characters genuinely getting to know each other. That's kinda the bedrock of any romance, and it's shocking how many series skip over it.
