(I edited below a bit since I just ended up buying his digital book and it contains the epilogue of the story.)
In the original timeline where Verniy had come from, the Admiral died (revealed to be a suicide by his own Derringer, from some accident occurred during the practice). She eventually went to Soviet Union, becoming Verniy. The future's fairies seem to develop a time travelling device, including the pocket watch that could create a back up of Verniy's memories, in case something happened.
Verniy traveled to the day that the Admiral died. She managed to stop the practice and left, dropping the pocket watch at that timeline.
The pocket watch was passed to Hibiki who somehow managed to unveil the memories locked inside (revealed to be with the compass girl's help).
Later on, Hibiki asked the compass girl to record her past memories with the Admiral, whom she chose to tell her feelings and finally marry him (what Verniy never has a chance to do so).
Knowing that two of them couldn't exist at the same time, Hibiki we saw at the start of the story chose to leave and let the returning Verniy has her happiness. She hid herself from others prior to Verniy's return, then vanished from existence with the compass girl sending her off.
The compass girl then passes the watch to Verniy. That let her realize of her younger self's sacrifice.
In the original timeline where Verniy had come from, the Admiral died during that practice. It is implied that later on Hibiki lost her sisters and eventually went to Soviet Union, becoming Verniy. The future's fairies seem to develop a time travelling device, including the pocket watch that could create a back up of Verniy's memories, in case something happened.
Verniy traveled to the day that the Admiral died. She managed to stop the practice and left, dropping the pocket watch at that timeline.
The pocket watch was passed to Hibiki who somehow managed to unveil the memories locked inside (maybe with compass girl's help). She used those memories to prevent many events up until Verniy's time, maybe including her sisters' death.
But Hibiki, knowing that two of them couldn't exist at the same time, chose to leave and let the returning Verniy has her happiness. Hibiki we saw at the start of the story then vanishes from existence.
It is implied that the compass girl will pass the watch to Verniy. That would let her realize of her younger self's sacrifice.
I know....Renewed story. Lost story.Yes....
Yes....We'll see each other again.
We'll surely see each other again.Remember "you", so please...But... I alone will definitely...Definitely, always...!!