Katekyo Hitman Reborn! A day to live and die.
Here there be spoilers for the TYL Arc and all that jazz. Also, the title is taken from the 31 Days theme for June 29, 2006.
They did not know this and because of twists and turns of a rewritable future they were never going to find out, but the Cloud Guardian had retained close contact with the Tenth Head of the Vongola Family all throughout their conflict with the Millefore – he had watched from his place in the fringes of the underworld, drawing up the connections where others would only see random family violence, monitoring the smuggling routes, poring over the reports of boxes retrieved and conspiracies hatched behind closed doors. He had sent word to the Vongola house just once, two months before the breakdown. Sawada Tsuyanoshi, of course, took things into stride, and sent Hibird back with a message bearing a single line: Please don't worry – everything will be all right.
Hibari Kyouya had been tempted to send back a scathing reply, but thought better of it. And he waited, telling himself that it wasn't because Tsuna had told him to but because writing back would have shown that he was affected and showing that he was affected was one step closer to showing that he cared, and that was not the sort of signal that he wanted to send. He waited, even as the reports grew worse and the allies to the Vongola Family began to fall, one by one. He waited until it became harder and harder to sleep at night, until the Storm Guardian's correspondences trickled to a complete stop and any man he sent in to check on the situation went back to him in pieces.
He came to Italy and arrived in time to see the Millefore setting the Vongola Mansion ablaze, and hear the screams of the people still trapped within. The rest of that evening was lost in memories of blood and smoke and the gray morning after, with Gokudera on his knees beside a newly made coffin and Yamamoto gripping his broken arm so hard his knuckles stood out, bone white against the fine black silk of his suit.
Hibari Kyouya paid his respects, withdrew, and waited again. His timing was a little better the second time around, but it did not prepare him for the jarring experience of encountering a ghost from the past. Looking into those eyes was harder than it should have been, for all he saw were promises, promises he had failed to keep.
Later, as the doors to the underground headquarters open and the blinding brilliance of the Millefore's floodlights greeted him, Hibari stared into the faces of the thousands he intended to bring down and wondered if this was his way of redeeming himself, and, if so, how effective would it be. He decided, as his fangs connected with the jawline of the first man who approached him, that if he survived tomorrow, he would ask the young boss himself.