Someone correct me on this if i am wrong.
Recounting, Ying and Bai Long were a couple/married.
Eventually Ying ended pregnant with Long's child.
Around that time in a date with Long, she asks him if he would go after her if her picture was the one in the envelope instead of Kyara's, and Long had the hubris of saying that it would have been interesting.
So Ying rightfully lefts him, knowing that if it came down to it she would lost and die, thus explaining why Long's nightmare had Ying saying that he was stronger, because that's one of the reasons she lefts him.
At that point Long didn't knew that Ying was pregnant (he probably wouldn't have said such a dumb thing otherwise).
While Ying was overseas she gave birth to their child, but the kid doesn't survive, something that stills haunts her to this day. It also seems like she was forcing herself to live until she could meet Long again and tell him the whole story.
After her miscarriage Ying decides to remain overseas, eventually changing her name to Mitaka Hana, or Taka for short, while Long went with his assassin business as usual, maybe?
Since Kyara never faced Long, maybe he retired the moment Taka left him? and he has been wanting to meet her ever since that day, regretting what he said? but that's way too romantic. But i do wonder why he didn't took the job to kill Kyara.
Anyway, at one point Long learns that Ying was pregnant with his child, but he never manages to find her or track her down.
The years went by, Long retires due to old age and boredom, becoming a legend, and a bunch of impersonators appear trying to fill the empty throne, while Taka joins the Private Funeral Division.
It also seems that Long believes the child survived? but that could be part of the nightmare, or could it be that he wants to kill Taka and then himself to have a reunion in the afterlife with their kid? or maybe he genuinely thinks that the 3 of them can start a nice life together?
Now in the present Taka has joined Kakerou as a referee, and in order to meet his ex-wife again Long takes Ideal's offer and joins them, but...
His reunion is less than Ideal (hehe get it), and the "reunion" if it can even be called that, ends being a one sided one.
Long gets killed by Taka without knowing that he had meet her, still submerged in his own nightmare or he did realize that he meet Ying again, but he was too weakened to even speak out his intentions.
@Ominous @MYW while Taka figures out that the ban intruder she was hunting was Long because of his characteristic fighting style that gives the impression of a mass of blades.
However now that Long's blade is all battered and no longer a threat to her,
it is already too late, she is a different person, with a different life, and their child has been gone for years.
Now that she is actually stronger than Long there's no reason for her to be with him, or for her to tell him why she really left.
After a silent look Taka puts her hat back on, and leaves, and their story together ends.
Wonder what happened to Gakuto? he was the one protecting Nico-chan but then Yakou ended being the one protecting her from a mob.